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/services/capacity_forecast_service.py

@@ -16,13 +16,14 @@ from decimal import Decimal
 from sqlalchemy import func
 from sqlalchemy.orm import Session
 
-from app.modules.catalog.models import Product
 from app.modules.billing.models import (
     CapacitySnapshot,
     MerchantSubscription,
     SubscriptionStatus,
 )
-from app.modules.tenancy.models import Store, StoreUser
+from app.modules.contracts.metrics import MetricsContext
+from app.modules.core.services.stats_aggregator import stats_aggregator
+from app.modules.tenancy.models import Platform, Store, StoreUser
 
 logger = logging.getLogger(__name__)
 
@@ -87,8 +88,17 @@ class CapacityForecastService:
             or 0
         )
 
-        # Resource metrics
-        total_products = db.query(func.count(Product.id)).scalar() or 0
+        # Resource metrics via provider pattern (avoids direct catalog/orders imports)
+        start_of_month = now.replace(day=1, hour=0, minute=0, second=0, microsecond=0)
+        platform = db.query(Platform).first()
+        platform_id = platform.id if platform else 1
+
+        stats = stats_aggregator.get_admin_stats_flat(
+            db, platform_id,
+            context=MetricsContext(date_from=start_of_month),
+        )
+
+        total_products = stats.get("catalog.total_products", 0)
         total_team = (
             db.query(func.count(StoreUser.id))
             .filter(StoreUser.is_active == True)  # noqa: E712
@@ -96,15 +106,8 @@ class CapacityForecastService:
             or 0
         )
 
-        # Orders this month
-        start_of_month = now.replace(day=1, hour=0, minute=0, second=0, microsecond=0)
-        from app.modules.orders.models import Order
-
-        total_orders = (
-            db.query(func.count(Order.id))
-            .filter(Order.created_at >= start_of_month)
-            .scalar() or 0
-        )
+        # Orders this month (from stats aggregator)
+        total_orders = stats.get("orders.in_period", 0)
 
         # Storage metrics
         try: