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>

middleware/platform_context.py

@@ -108,7 +108,10 @@ class PlatformContextManager:
 
         # Method 3: Default platform for localhost without /platforms/ prefix
         # This serves the main marketing site
+        # Store routes require explicit platform via /platforms/{code}/store/...
         if host_without_port in ["localhost", "127.0.0.1"]:
+            if path.startswith(("/store/", "/stores/")):
+                return None  # No platform — handlers will show appropriate error
             return {
                 "path_prefix": DEFAULT_PLATFORM_CODE,
                 "detection_method": "default",
@@ -138,6 +141,7 @@ class PlatformContextManager:
         if context.get("detection_method") == "domain":
             domain = context.get("domain")
             if domain:
+                # Try Platform.domain first
                 platform = (
                     db.query(Platform)
                     .filter(Platform.domain == domain)
@@ -150,6 +154,26 @@ class PlatformContextManager:
                         f"[PLATFORM] Platform found via domain: {domain} → {platform.name}"
                     )
                     return platform
+
+                # Fallback: Check StoreDomain for custom store domains
+                from app.modules.tenancy.models import StoreDomain
+                store_domain = (
+                    db.query(StoreDomain)
+                    .filter(StoreDomain.domain == domain, StoreDomain.is_active.is_(True))
+                    .first()
+                )
+                if store_domain and store_domain.platform_id:
+                    platform = (
+                        db.query(Platform)
+                        .filter(Platform.id == store_domain.platform_id, Platform.is_active.is_(True))
+                        .first()
+                    )
+                    if platform:
+                        logger.debug(
+                            f"[PLATFORM] Platform found via store domain: {domain} → {platform.name}"
+                        )
+                        return platform
+
                 logger.debug(f"[PLATFORM] No platform found for domain: {domain}")
 
         # Method 2: Path-prefix lookup
@@ -399,7 +423,10 @@ class PlatformContextMiddleware:
                 }
 
         # Method 3: Default for localhost - serves main marketing site
+        # Store routes require explicit platform via /platforms/{code}/store/...
         if host_without_port in ["localhost", "127.0.0.1"]:
+            if path.startswith(("/store/", "/stores/")):
+                return None  # No platform — handlers will show appropriate error
             return {
                 "path_prefix": DEFAULT_PLATFORM_CODE,
                 "detection_method": "default",