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/analytics/services/__init__.py

@@ -9,26 +9,9 @@ from app.modules.analytics.services.stats_service import (
     stats_service,
     StatsService,
 )
-from app.modules.analytics.services.usage_service import (
-    usage_service,
-    UsageService,
-    UsageData,
-    UsageMetricData,
-    TierInfoData,
-    UpgradeTierData,
-    LimitCheckData,
-)
 
 __all__ = [
     # Stats service
     "stats_service",
     "StatsService",
-    # Usage service
-    "usage_service",
-    "UsageService",
-    "UsageData",
-    "UsageMetricData",
-    "TierInfoData",
-    "UpgradeTierData",
-    "LimitCheckData",
 ]