feat(subscriptions): migrate subscription management to merchant level and seed tiers

Move subscription create/edit from store detail (broken endpoint) to merchant
detail page with proper modal UI. Seed 4 subscription tiers (Essential,
Professional, Business, Enterprise) in init_production.py. Also includes
cross-module dependency declarations, store domain platform_id migration,
platform context middleware, CMS route fixes, and migration backups.

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

app/modules/cms/routes/api/storefront.py

@@ -36,11 +36,13 @@ def get_navigation_pages(request: Request, db: Session = Depends(get_db)):
     Returns store overrides + platform defaults.
     """
     store = getattr(request.state, "store", None)
+    platform = getattr(request.state, "platform", None)
     store_id = store.id if store else None
+    platform_id = platform.id if platform else 1
 
     # Get all published pages for this store
     pages = content_page_service.list_pages_for_store(
-        db, store_id=store_id, include_unpublished=False
+        db, platform_id=platform_id, store_id=store_id, include_unpublished=False
     )
 
     return [
@@ -64,10 +66,13 @@ def get_content_page(slug: str, request: Request, db: Session = Depends(get_db))
     Returns store override if exists, otherwise platform default.
     """
     store = getattr(request.state, "store", None)
+    platform = getattr(request.state, "platform", None)
     store_id = store.id if store else None
+    platform_id = platform.id if platform else 1
 
     page = content_page_service.get_page_for_store_or_raise(
         db,
+        platform_id=platform_id,
         slug=slug,
         store_id=store_id,
         include_unpublished=False,  # Only show published pages