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/testing/README.md

@@ -0,0 +1,56 @@
+# 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]