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/inventory/definition.py

@@ -52,6 +52,7 @@ inventory_module = ModuleDefinition(
         "transaction history, and bulk imports."
     ),
     version="1.0.0",
+    requires=["catalog"],  # Depends on catalog module for Product model
     # Module-driven permissions
     permissions=[
         PermissionDefinition(