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>

docs/ROADMAP.md

@@ -57,10 +57,10 @@
 
 | Task | Priority | Effort | Status |
 |------|----------|--------|--------|
-| HTTP server effect | P1 | 2 weeks | ❌ Missing |
+| HTTP server effect | P1 | 2 weeks | ✅ Complete |
 | Routing DSL | P2 | 1 week | ❌ Missing |
 | Middleware pattern | P2 | 1 week | ❌ Missing |
-| Request/Response types | P1 | 3 days | ❌ Missing |
+| Request/Response types | P1 | 3 days | ✅ Complete (via HttpServer effect) |
 
 ### Phase 1.4: Developer Experience