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

@@ -0,0 +1,58 @@
+# 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