feat: add HTTP framework with routing and JSON helpers

- Add stdlib/http.lux with:
  - Response builders (httpOk, httpNotFound, etc.)
  - Path pattern matching with parameter extraction
  - JSON construction helpers (jsonStr, jsonNum, jsonObj, etc.)
- Add examples/http_api.lux demonstrating a complete REST API
- Add examples/http_router.lux showing the routing pattern
- Update stdlib/lib.lux to include http module

The framework provides functional building blocks for web apps:
- Route matching: pathMatches("/users/:id", path)
- Path params: getPathSegment(path, 1)
- Response building: httpOk(jsonObj(...))

Note: Due to current type system limitations with type aliases
and function types, the framework uses inline types rather
than abstract Request/Response types.

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

examples/http_router.lux

@@ -0,0 +1,98 @@
+// HTTP Router Example
+//
+// Demonstrates the HTTP helper library with:
+// - Path pattern matching
+// - Response builders
+// - JSON helpers
+//
+// Run with: lux examples/http_router.lux
+// Test with:
+//   curl http://localhost:8080/
+//   curl http://localhost:8080/users
+//   curl http://localhost:8080/users/42
+
+import stdlib/http
+
+// ============================================================
+// Route Handlers
+// ============================================================
+
+fn indexHandler(): { status: Int, body: String } =
+    httpOk("Welcome to Lux HTTP Framework!")
+
+fn listUsersHandler(): { status: Int, body: String } = {
+    let user1 = jsonObject(jsonJoin([jsonNumber("id", 1), jsonString("name", "Alice")]))
+    let user2 = jsonObject(jsonJoin([jsonNumber("id", 2), jsonString("name", "Bob")]))
+    let users = jsonArray(jsonJoin([user1, user2]))
+    httpOk(users)
+}
+
+fn getUserHandler(path: String): { status: Int, body: String } = {
+    match getPathSegment(path, 1) {
+        Some(id) => {
+            let body = jsonObject(jsonJoin([jsonString("id", id), jsonString("name", "User " + id)]))
+            httpOk(body)
+        },
+        None => httpNotFound(jsonErrorMsg("User ID required"))
+    }
+}
+
+fn healthHandler(): { status: Int, body: String } =
+    httpOk(jsonObject(jsonString("status", "healthy")))
+
+// ============================================================
+// Router
+// ============================================================
+
+fn router(method: String, path: String, body: String): { status: Int, body: String } = {
+    if method == "GET" && path == "/" then indexHandler()
+    else if method == "GET" && path == "/health" then healthHandler()
+    else if method == "GET" && path == "/users" then listUsersHandler()
+    else if method == "GET" && pathMatches(path, "/users/:id") then getUserHandler(path)
+    else httpNotFound(jsonErrorMsg("Not found: " + path))
+}
+
+// ============================================================
+// Server
+// ============================================================
+
+fn serveLoop(remaining: Int): Unit with {Console, HttpServer} = {
+    if remaining <= 0 then {
+        Console.print("Max requests reached, stopping server.")
+        HttpServer.stop()
+    } else {
+        let req = HttpServer.accept()
+        Console.print(req.method + " " + req.path)
+        let resp = router(req.method, req.path, req.body)
+        HttpServer.respond(resp.status, resp.body)
+        serveLoop(remaining - 1)
+    }
+}
+
+fn main(): Unit with {Console, HttpServer} = {
+    let port = 8080
+    let maxRequests = 10
+    Console.print("========================================")
+    Console.print("  Lux HTTP Router Demo")
+    Console.print("========================================")
+    Console.print("")
+    Console.print("Endpoints:")
+    Console.print("  GET /           - Welcome message")
+    Console.print("  GET /health     - Health check")
+    Console.print("  GET /users      - List all users")
+    Console.print("  GET /users/:id  - Get user by ID")
+    Console.print("")
+    Console.print("Try:")
+    Console.print("  curl http://localhost:8080/")
+    Console.print("  curl http://localhost:8080/users")
+    Console.print("  curl http://localhost:8080/users/42")
+    Console.print("")
+    Console.print("Starting server on port " + toString(port) + "...")
+    Console.print("Will handle " + toString(maxRequests) + " requests then stop.")
+    Console.print("")
+    HttpServer.listen(port)
+    Console.print("Server listening!")
+    serveLoop(maxRequests)
+}
+
+let output = run main() with {}