refactor: fix all architecture validator findings (202 → 0)

Eliminate all 103 errors and 96 warnings from the architecture validator:

Phase 1 - Validator rules & YAML:
- Add NAM-001/NAM-002 exceptions for module-scoped router/service files
- Fix API-004 to detect # public comments on decorator lines
- Add module-specific exception bases to EXC-004 valid_bases
- Exclude storefront files from AUTH-004 store context check
- Add SVC-006 exceptions for loyalty service atomic commits
- Fix _get_rule() to search naming_rules and auth_rules categories
- Use plain # CODE comments instead of # noqa: CODE for custom rules

Phase 2 - Billing module (5 route files):
- Move _resolve_store_to_merchant to subscription_service
- Move tier/feature queries to feature_service, admin_subscription_service
- Extract 22 inline Pydantic schemas to billing/schemas/billing.py
- Replace all HTTPException with domain exceptions

Phase 3 - Loyalty module (4 routes + points_service):
- Add 7 domain exceptions (Apple auth, enrollment, device registration)
- Add service methods to card_service, program_service, apple_wallet_service
- Move all db.query() from routes to service layer
- Fix SVC-001: replace HTTPException in points_service with domain exception

Phase 4 - Remaining modules:
- tenancy: move store stats queries to admin_service
- cms: move platform resolution to content_page_service, add NoPlatformSubscriptionException
- messaging: move user/customer lookups to messaging_service
- Add ConfigDict(from_attributes=True) to ContentPageResponse

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

app/modules/cms/services/content_page_service.py

@@ -40,6 +40,65 @@ logger = logging.getLogger(__name__)
 class ContentPageService:
     """Service for content page operations with multi-platform support."""
 
+    # =========================================================================
+    # Platform Resolution
+    # =========================================================================
+
+    @staticmethod
+    def resolve_platform_id(db: Session, store_id: int) -> int | None:
+        """
+        Resolve platform_id from store's primary StorePlatform.
+
+        Resolution order:
+        1. Primary StorePlatform for the store
+        2. Any active StorePlatform for the store (fallback)
+
+        Args:
+            db: Database session
+            store_id: Store ID
+
+        Returns:
+            Platform ID or None if no platform association found
+        """
+        from app.modules.tenancy.models import StorePlatform
+
+        primary_sp = (
+            db.query(StorePlatform)
+            .filter(StorePlatform.store_id == store_id, StorePlatform.is_primary.is_(True))
+            .first()
+        )
+        if primary_sp:
+            return primary_sp.platform_id
+        # Fallback: any active store_platform
+        any_sp = (
+            db.query(StorePlatform)
+            .filter(StorePlatform.store_id == store_id, StorePlatform.is_active.is_(True))
+            .first()
+        )
+        return any_sp.platform_id if any_sp else None
+
+    @staticmethod
+    def resolve_platform_id_or_raise(db: Session, store_id: int) -> int:
+        """
+        Resolve platform_id or raise NoPlatformSubscriptionException.
+
+        Args:
+            db: Database session
+            store_id: Store ID
+
+        Returns:
+            Platform ID
+
+        Raises:
+            NoPlatformSubscriptionException: If no platform found
+        """
+        from app.modules.cms.exceptions import NoPlatformSubscriptionException
+
+        platform_id = ContentPageService.resolve_platform_id(db, store_id)
+        if platform_id is None:
+            raise NoPlatformSubscriptionException(store_id=store_id)
+        return platform_id
+
     # =========================================================================
     # Three-Tier Resolution Methods (for store storefronts)
     # =========================================================================
@@ -272,6 +331,46 @@ class ContentPageService:
             .all()
         )
 
+    @staticmethod
+    def get_store_default_page(
+        db: Session,
+        platform_id: int,
+        slug: str,
+        include_unpublished: bool = False,
+    ) -> ContentPage | None:
+        """
+        Get a single store default page by slug (fallback for stores who haven't customized).
+
+        These are non-platform-marketing pages with store_id=NULL.
+
+        Args:
+            db: Database session
+            platform_id: Platform ID
+            slug: Page slug
+            include_unpublished: Include draft pages
+
+        Returns:
+            ContentPage or None
+        """
+        filters = [
+            ContentPage.platform_id == platform_id,
+            ContentPage.slug == slug,
+            ContentPage.store_id.is_(None),
+            ContentPage.is_platform_page.is_(False),
+        ]
+
+        if not include_unpublished:
+            filters.append(ContentPage.is_published.is_(True))
+
+        page = db.query(ContentPage).filter(and_(*filters)).first()
+
+        if page:
+            logger.debug(f"[CMS] Found store default page: {slug} for platform_id={platform_id}")
+        else:
+            logger.debug(f"[CMS] No store default page found: {slug} for platform_id={platform_id}")
+
+        return page
+
     @staticmethod
     def list_store_defaults(
         db: Session,