fix(billing): resolve 3 IMPORT-001 architecture violations in billing module

Replace direct imports from optional modules (catalog, orders, analytics)
with provider pattern calls (stats_aggregator, feature_aggregator) and
move usage_service from analytics to billing where it belongs.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/modules/billing/routes/api/store_usage.py

@@ -18,7 +18,7 @@ from sqlalchemy.orm import Session
 
 from app.api.deps import get_current_store_api, require_module_access
 from app.core.database import get_db
-from app.modules.analytics.services.usage_service import usage_service
+from app.modules.billing.services.usage_service import usage_service
 from app.modules.enums import FrontendType
 from models.schema.auth import UserContext