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/stripe_service.py

@@ -10,7 +10,10 @@ Provides:
 - Webhook event construction
 """
 
+from __future__ import annotations
+
 import logging
+from typing import TYPE_CHECKING
 
 import stripe
 from sqlalchemy.orm import Session
@@ -23,7 +26,9 @@ from app.modules.billing.exceptions import (
 from app.modules.billing.models import (
     MerchantSubscription,
 )
-from app.modules.tenancy.models import Store
+
+if TYPE_CHECKING:
+    from app.modules.tenancy.models import Store
 
 logger = logging.getLogger(__name__)
 
@@ -294,10 +299,10 @@ class StripeService:
         self._check_configured()
 
         # Get or create Stripe customer
-        from app.modules.tenancy.models import StorePlatform
+        from app.modules.tenancy.services.platform_service import platform_service
+        from app.modules.tenancy.services.team_service import team_service
 
-        sp = db.query(StorePlatform.platform_id).filter(StorePlatform.store_id == store.id).first()
-        platform_id = sp[0] if sp else None
+        platform_id = platform_service.get_primary_platform_id_for_store(db, store.id)
         subscription = None
         if store.merchant_id and platform_id:
             subscription = (
@@ -313,16 +318,7 @@ class StripeService:
             customer_id = subscription.stripe_customer_id
         else:
             # Get store owner email
-            from app.modules.tenancy.models import StoreUser
-
-            owner = (
-                db.query(StoreUser)
-                .filter(
-                    StoreUser.store_id == store.id,
-                    StoreUser.is_owner == True,
-                )
-                .first()
-            )
+            owner = team_service.get_store_owner(db, store.id)
             email = owner.user.email if owner and owner.user else None
 
             customer_id = self.create_customer(store, email or f"{store.store_code}@placeholder.com")