fix: add database migrations at container startup and deployment tests

feat: migrate from TypedDict to Pydantic for type safety

feat: enable DRF browsable API and add root redirect

fix: add HuggingFace Space domain to ALLOWED_HOSTS

fix: replace ThreadPoolExecutor with SynchronousExecutor for SQLite compatibility

fix: replace parallel ThreadPoolExecutor with single-worker serial execution

feat: implement TDD for Wall Construction API with full type safety