feat: add schema evolution type system integration and HTTP server effect

Schema Evolution:
- Preserve version info in type resolution (Type::Versioned)
- Track versioned type declarations in typechecker
- Detect version mismatches at compile time (@v1 vs @v2 errors)
- Support @v2+ (at least) and @latest version constraints
- Store migrations for future auto-migration support
- Fix let bindings to preserve declared type annotations

HTTP Server Effect:
- Add HttpServer effect with listen, accept, respond, respondWithHeaders, stop
- Implement blocking request handling via tiny_http
- Request record includes method, path, body, headers
- Add http_server.lux example with routing via pattern matching
- Add type-checking test for HttpServer effect

Tests: 222 passing (up from 217)

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

examples/http_server.lux

@@ -0,0 +1,48 @@
+// HTTP Server Example
+// Run with: cargo run -- examples/http_server.lux
+// Then visit: http://localhost:8080/
+
+// Simple request handler
+fn handleRequest(req: { method: String, path: String, body: String, headers: List<(String, String)> }): Unit with {Console, HttpServer} = {
+    Console.print("Received: " + req.method + " " + req.path)
+
+    // Route based on path
+    match req.path {
+        "/" => HttpServer.respond(200, "Welcome to Lux HTTP Server!"),
+        "/hello" => HttpServer.respond(200, "Hello, World!"),
+        "/json" => HttpServer.respondWithHeaders(
+            200,
+            "{\"message\": \"Hello from Lux!\"}",
+            [("Content-Type", "application/json")]
+        ),
+        "/echo" => HttpServer.respond(200, "You sent: " + req.body),
+        _ => HttpServer.respond(404, "Not Found: " + req.path)
+    }
+}
+
+// Handle N requests then stop
+fn serveN(n: Int): Unit with {Console, HttpServer} =
+    if n <= 0 then {
+        Console.print("Server stopping...")
+        HttpServer.stop()
+    } else {
+        let req = HttpServer.accept()
+        handleRequest(req)
+        serveN(n - 1)
+    }
+
+// Main entry point
+fn main(): Unit with {Console, HttpServer} = {
+    let port = 8080
+    Console.print("Starting HTTP server on port " + toString(port) + "...")
+    HttpServer.listen(port)
+    Console.print("Server listening! Will handle 5 requests then stop.")
+    Console.print("Try: curl http://localhost:8080/")
+    Console.print("     curl http://localhost:8080/hello")
+    Console.print("     curl http://localhost:8080/json")
+    Console.print("     curl -X POST -d 'test data' http://localhost:8080/echo")
+    serveN(5)
+}
+
+// Run main
+main()