refactor: add infrastructure dependency injection to pypi_proxy

Add dependency injection helper functions for HttpClientManager
and CacheService, along with imports for the new infrastructure
modules (http_client, cache_service, db_utils).

backend/app/pypi_proxy.py

@@ -26,12 +26,25 @@ from .database import get_db
 from .models import UpstreamSource, CachedUrl, Artifact, Project, Package, PackageVersion, ArtifactDependency
 from .storage import S3Storage, get_storage
 from .config import get_env_upstream_sources, get_settings
+from .http_client import HttpClientManager
+from .cache_service import CacheService, CacheCategory
+from .db_utils import ArtifactRepository
 
 logger = logging.getLogger(__name__)
 
 router = APIRouter(prefix="/pypi", tags=["pypi-proxy"])
 
 
+def get_http_client(request: Request) -> HttpClientManager:
+    """Get HttpClientManager from app state."""
+    return request.app.state.http_client
+
+
+def get_cache(request: Request) -> CacheService:
+    """Get CacheService from app state."""
+    return request.app.state.cache
+
+
 # Timeout configuration for proxy requests
 PROXY_CONNECT_TIMEOUT = 30.0
 PROXY_READ_TIMEOUT = 60.0