refactor(arch): eliminate all cross-module model imports in service layer

Enforce MOD-025/MOD-026 rules: zero top-level cross-module model imports
remain in any service file. All 66 files migrated using deferred import
patterns (method-body, _get_model() helpers, instance-cached self._Model)
and new cross-module service methods in tenancy. Documentation updated
with Pattern 6 (deferred imports), migration plan marked complete, and
violations status reflects 84→0 service-layer violations.

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

app/modules/billing/services/feature_service.py

@@ -115,21 +115,15 @@ class FeatureService:
         Returns:
             Tuple of (merchant_id, platform_id), either may be None
         """
-        from app.modules.tenancy.models import Store, StorePlatform
+        from app.modules.tenancy.services.platform_service import platform_service
+        from app.modules.tenancy.services.store_service import store_service
 
-        store = db.query(Store).filter(Store.id == store_id).first()
+        store = store_service.get_store_by_id_optional(db, store_id)
         if not store:
             return None, None
 
         merchant_id = store.merchant_id
-        # Get primary platform_id from StorePlatform junction
-        sp = (
-            db.query(StorePlatform.platform_id)
-            .filter(StorePlatform.store_id == store_id, StorePlatform.is_active == True)  # noqa: E712
-            .order_by(StorePlatform.is_primary.desc())
-            .first()
-        )
-        platform_id = sp[0] if sp else None
+        platform_id = platform_service.get_primary_platform_id_for_store(db, store_id)
 
         return merchant_id, platform_id
 
@@ -142,19 +136,14 @@ class FeatureService:
         Returns all active platform IDs for the store's merchant,
         ordered with the primary platform first.
         """
-        from app.modules.tenancy.models import Store, StorePlatform
+        from app.modules.tenancy.services.platform_service import platform_service
+        from app.modules.tenancy.services.store_service import store_service
 
-        store = db.query(Store).filter(Store.id == store_id).first()
+        store = store_service.get_store_by_id_optional(db, store_id)
         if not store:
             return None, []
 
-        platform_ids = [
-            sp[0]
-            for sp in db.query(StorePlatform.platform_id)
-            .filter(StorePlatform.store_id == store_id, StorePlatform.is_active == True)  # noqa: E712
-            .order_by(StorePlatform.is_primary.desc())
-            .all()
-        ]
+        platform_ids = platform_service.get_active_platform_ids_for_store(db, store_id)
         return store.merchant_id, platform_ids
 
     def _get_subscription(