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/lib.lux

@@ -0,0 +1,72 @@
+// 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)
+}