refactor(proxy): move proxy logic to services.mitmproxy and update Docker service model

- Rename DockerService to DockerContainer and add folder attribute
- Move proxy-related modules (models, validator) to services.mitmproxy
- Update imports and references to new module locations
- Refactor Docker utilities to use DockerContainer and improve service discovery
- Add manager.py with create_proxy utility stub
- Initialize discovered Docker services at app startup and warn if none found

app/api/proxy/router.py

@@ -11,7 +11,7 @@ from repositories.proxy import (
 from repositories.proxy import (
     list_proxies as list_proxy_documents,
 )
-from services.proxy.validator import ProxyCodeValidationError, validate_proxy_code
+from services.mitmproxy.validator import ProxyCodeValidationError, validate_proxy_code
 
 router = APIRouter(
     prefix="/proxy",