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>

Cargo.toml

@@ -14,6 +14,7 @@ serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 rand = "0.8"
 reqwest = { version = "0.11", features = ["blocking", "json"] }
+tiny_http = "0.12"
 
 # Cranelift for native compilation
 cranelift-codegen = "0.95"