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/cms/services/store_theme_service.py

@@ -6,6 +6,8 @@ Business logic for store theme management.
 Handles theme CRUD operations, preset application, and validation.
 """
 
+from __future__ import annotations
+
 import logging
 import re
 
@@ -29,7 +31,6 @@ from app.modules.cms.services.theme_presets import (
     get_preset_preview,
 )
 from app.modules.tenancy.exceptions import StoreNotFoundException
-from app.modules.tenancy.models import Store
 
 logger = logging.getLogger(__name__)
 
@@ -67,9 +68,9 @@ class StoreThemeService:
         Raises:
             StoreNotFoundException: If store not found
         """
-        store = (
-            db.query(Store).filter(Store.store_code == store_code.upper()).first()
-        )
+        from app.modules.tenancy.services.store_service import store_service
+
+        store = store_service.get_store_by_code(db, store_code)
 
         if not store:
             self.logger.warning(f"Store not found: {store_code}")