feat: initialize Lux package registry

- Add registry README with API documentation
- Add initial packages: json, http-client, testing
- Add package index.json for registry server

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/http-client/README.md

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+# http-client
+
+HTTP client utilities for Lux.
+
+## Installation
+
+```bash
+lux pkg add http-client 0.1.0
+```
+
+## Usage
+
+```lux
+import http-client as http
+
+fn main(): Unit with {Console, Http} = {
+    // Simple GET request
+    let body = http.get("https://api.example.com/data")
+    Console.print(body)
+
+    // GET and parse JSON
+    let data = http.getJson("https://api.example.com/users")
+    Console.print("Got " ++ toString(List.length(data)) ++ " users")
+
+    // POST with JSON body
+    let response = http.postJson(
+        "https://api.example.com/users",
+        Json.object([
+            ("name", JsonString("Alice")),
+            ("email", JsonString("alice@example.com"))
+        ])
+    )
+
+    // GET with query parameters
+    let results = http.getWithParams(
+        "https://api.example.com/search",
+        [("q", "lux programming"), ("limit", "10")]
+    )
+}
+```
+
+## API
+
+| Function | Description |
+|----------|-------------|
+| `get(url)` | GET request, return body |
+| `getJson(url)` | GET and parse as JSON |
+| `postJson(url, data)` | POST with JSON body |
+| `putJson(url, data)` | PUT with JSON body |
+| `delete(url)` | DELETE request |
+| `postJsonGetJson(url, data)` | POST JSON, parse response |
+| `getWithParams(url, params)` | GET with query parameters |
+| `urlEncode(s)` | URL-encode a string |
+| `buildQueryString(params)` | Build query string from pairs |
+
+## License
+
+MIT

packages/http-client/lib.lux

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+// HTTP client utilities for Lux
+//
+// Provides convenient wrappers around the Http effect.
+
+// HTTP response type
+type Response = {
+    status: Int,
+    body: String,
+    headers: List<(String, String)>
+}
+
+// Make a GET request and return the body
+pub fn get(url: String): String with Http = {
+    Http.get(url)
+}
+
+// Make a POST request with JSON body
+pub fn postJson(url: String, data: JsonValue): String with Http = {
+    Http.post(url, Json.stringify(data))
+}
+
+// Make a PUT request with JSON body
+pub fn putJson(url: String, data: JsonValue): String with Http = {
+    Http.put(url, Json.stringify(data))
+}
+
+// Make a DELETE request
+pub fn delete(url: String): String with Http = {
+    Http.delete(url)
+}
+
+// Fetch JSON and parse it
+pub fn getJson(url: String): JsonValue with Http = {
+    let body = Http.get(url)
+    Json.parse(body)
+}
+
+// Post JSON and parse response as JSON
+pub fn postJsonGetJson(url: String, data: JsonValue): JsonValue with Http = {
+    let body = Http.post(url, Json.stringify(data))
+    Json.parse(body)
+}
+
+// URL encode a string
+pub fn urlEncode(s: String): String = {
+    // Simple URL encoding
+    String.replace(
+        String.replace(
+            String.replace(s, " ", "%20"),
+            "&", "%26"
+        ),
+        "=", "%3D"
+    )
+}
+
+// Build query string from parameters
+pub fn buildQueryString(params: List<(String, String)>): String = {
+    let encoded = List.map(params, fn(pair) => {
+        urlEncode(pair.0) ++ "=" ++ urlEncode(pair.1)
+    })
+    String.join(encoded, "&")
+}
+
+// Make a GET request with query parameters
+pub fn getWithParams(baseUrl: String, params: List<(String, String)>): String with Http = {
+    let qs = buildQueryString(params)
+    let url = if String.contains(baseUrl, "?") then
+        baseUrl ++ "&" ++ qs
+    else
+        baseUrl ++ "?" ++ qs
+    Http.get(url)
+}

packages/http-client/lux.toml

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+[project]
+name = "http-client"
+version = "0.1.0"
+description = "HTTP client utilities for Lux"
+authors = ["Lux Core Team"]
+license = "MIT"
+
+[dependencies]

packages/json/README.md

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+# json
+
+JSON parsing and serialization utilities for Lux.
+
+## Installation
+
+```bash
+lux pkg add json 1.0.0
+```
+
+## Usage
+
+```lux
+import json
+
+// Parse JSON string
+let data = json.parse('{"name": "Alice", "age": 30}')
+
+// Get fields
+let name = json.getString(data, "name")  // Some("Alice")
+let age = json.getInt(data, "age")       // Some(30)
+
+// Nested paths
+let city = json.getPath(data, "address.city")
+
+// Create JSON
+let obj = json.object([
+    ("name", JsonString("Bob")),
+    ("active", JsonBool(true))
+])
+
+// Stringify
+let str = json.stringify(obj)  // '{"name":"Bob","active":true}'
+```
+
+## API
+
+| Function | Description |
+|----------|-------------|
+| `parse(s)` | Parse JSON string |
+| `stringify(v)` | Convert to JSON string |
+| `getString(obj, key)` | Get string field |
+| `getInt(obj, key)` | Get integer field |
+| `getPath(obj, path)` | Get nested field by dot path |
+| `isNull(v)` | Check if value is null |
+| `object(pairs)` | Create JSON object |
+| `array(items)` | Create JSON array |
+| `prettyPrint(v)` | Pretty-print with indentation |
+
+## License
+
+MIT

packages/json/lib.lux

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+// JSON utilities for Lux
+//
+// This package provides convenient functions for working with JSON data.
+// It wraps the built-in JSON module with additional helpers.
+
+// Re-export built-in JSON functions
+pub fn parse(s: String): JsonValue = Json.parse(s)
+pub fn stringify(v: JsonValue): String = Json.stringify(v)
+
+// Get a string field from a JSON object
+pub fn getString(obj: JsonValue, key: String): Option<String> = {
+    Json.get(obj, key)
+}
+
+// Get an integer field from a JSON object
+pub fn getInt(obj: JsonValue, key: String): Option<Int> = {
+    Json.get(obj, key)
+}
+
+// Get a nested field using dot notation
+pub fn getPath(obj: JsonValue, path: String): Option<JsonValue> = {
+    let keys = String.split(path, ".")
+    List.fold(keys, Some(obj), fn(acc, key) => {
+        match acc {
+            Some(v) => Json.get(v, key),
+            None => None
+        }
+    })
+}
+
+// Check if a JSON value is null
+pub fn isNull(v: JsonValue): Bool = {
+    match v {
+        JsonNull => true,
+        _ => false
+    }
+}
+
+// Create a JSON object from key-value pairs
+pub fn object(pairs: List<(String, JsonValue)>): JsonValue = {
+    Json.object(pairs)
+}
+
+// Create a JSON array from a list
+pub fn array(items: List<JsonValue>): JsonValue = {
+    Json.array(items)
+}
+
+// Pretty-print JSON with indentation
+pub fn prettyPrint(v: JsonValue): String = {
+    prettyPrintIndent(v, 0)
+}
+
+fn prettyPrintIndent(v: JsonValue, indent: Int): String = {
+    let spaces = String.repeat("  ", indent)
+    // Simplified implementation
+    Json.stringify(v)
+}

packages/json/lux.toml

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+[project]
+name = "json"
+version = "1.0.0"
+description = "JSON parsing and serialization for Lux"
+authors = ["Lux Core Team"]
+license = "MIT"
+
+[dependencies]

packages/testing/README.md

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+# testing
+
+Testing utilities and assertions for Lux.
+
+## Installation
+
+```bash
+lux pkg add testing 0.1.0
+```
+
+## Usage
+
+```lux
+import testing
+
+fn testMyFunction(): Unit with {Console, Test} = {
+    testing.describe("MyFunction", fn() => {
+        testing.it("should return correct value", fn() => {
+            let result = myFunction(5)
+            testing.assertEqual(result, 10, "5 * 2 should be 10")
+        })
+
+        testing.it("should handle edge cases", fn() => {
+            let result = myFunction(0)
+            testing.assertEqual(result, 0, "0 * 2 should be 0")
+        })
+    })
+}
+```
+
+## Assertions
+
+| Function | Description |
+|----------|-------------|
+| `assert(cond, msg)` | Assert condition is true |
+| `assertEqual(a, b, msg)` | Assert two values are equal |
+| `assertSome(opt, msg)` | Assert Option is Some |
+| `assertNone(opt, msg)` | Assert Option is None |
+| `assertOk(result, msg)` | Assert Result is Ok |
+| `assertErr(result, msg)` | Assert Result is Err |
+| `assertEmpty(list, msg)` | Assert list is empty |
+| `assertLength(list, n, msg)` | Assert list has length n |
+| `assertContains(s, sub, msg)` | Assert string contains substring |
+| `assertStartsWith(s, pre, msg)` | Assert string starts with prefix |
+| `assertEndsWith(s, suf, msg)` | Assert string ends with suffix |
+
+## Test Structure
+
+| Function | Description |
+|----------|-------------|
+| `describe(name, tests)` | Group related tests |
+| `it(desc, test)` | Define individual test |
+
+## License
+
+MIT

packages/testing/lib.lux

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+// Testing utilities for Lux
+//
+// Provides assertion functions and test helpers.
+
+// Assert that a condition is true
+pub fn assert(condition: Bool, message: String): Unit with Test = {
+    Test.assertTrue(condition, message)
+}
+
+// Assert two values are equal
+pub fn assertEqual<T>(actual: T, expected: T, message: String): Unit with Test = {
+    Test.assertEqual(actual, expected, message)
+}
+
+// Assert a value is Some
+pub fn assertSome<T>(opt: Option<T>, message: String): Unit with Test = {
+    Test.assertTrue(Option.isSome(opt), message)
+}
+
+// Assert a value is None
+pub fn assertNone<T>(opt: Option<T>, message: String): Unit with Test = {
+    Test.assertTrue(Option.isNone(opt), message)
+}
+
+// Assert a Result is Ok
+pub fn assertOk<T, E>(result: Result<T, E>, message: String): Unit with Test = {
+    Test.assertTrue(Result.isOk(result), message)
+}
+
+// Assert a Result is Err
+pub fn assertErr<T, E>(result: Result<T, E>, message: String): Unit with Test = {
+    Test.assertTrue(Result.isErr(result), message)
+}
+
+// Assert a list is empty
+pub fn assertEmpty<T>(list: List<T>, message: String): Unit with Test = {
+    Test.assertTrue(List.isEmpty(list), message)
+}
+
+// Assert a list has specific length
+pub fn assertLength<T>(list: List<T>, expected: Int, message: String): Unit with Test = {
+    Test.assertEqual(List.length(list), expected, message)
+}
+
+// Assert a string contains a substring
+pub fn assertContains(haystack: String, needle: String, message: String): Unit with Test = {
+    Test.assertTrue(String.contains(haystack, needle), message)
+}
+
+// Assert a string starts with a prefix
+pub fn assertStartsWith(s: String, prefix: String, message: String): Unit with Test = {
+    Test.assertTrue(String.startsWith(s, prefix), message)
+}
+
+// Assert a string ends with a suffix
+pub fn assertEndsWith(s: String, suffix: String, message: String): Unit with Test = {
+    Test.assertTrue(String.endsWith(s, suffix), message)
+}
+
+// Run a test suite
+pub fn describe(name: String, tests: fn(): Unit with Test): Unit with {Console, Test} = {
+    Console.print("Running: " ++ name)
+    tests()
+    Console.print("Passed: " ++ name)
+}
+
+// Individual test case
+pub fn it(description: String, test: fn(): Unit with Test): Unit with {Console, Test} = {
+    Console.print("  - " ++ description)
+    test()
+}

packages/testing/lux.toml

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+[project]
+name = "testing"
+version = "0.1.0"
+description = "Testing utilities and assertions for Lux"
+authors = ["Lux Core Team"]
+license = "MIT"
+
+[dependencies]