feat: complete dynamic menu system across all frontends

- Add "Merchant Frontend" tab to admin menu-config page
- Merchant render endpoint now respects AdminMenuConfig visibility
  via get_merchant_primary_platform_id() platform resolution
- New store menu render endpoint (GET /store/core/menu/render/store)
  with platform-scoped visibility and store_code interpolation
- Store sidebar migrated from hardcoded Jinja2 macros to dynamic
  Alpine.js x-for rendering with loading skeleton and fallback
- Store init-alpine.js: add loadMenuConfig(), expandSectionForCurrentPage()
- Include store page route fixes, login template updates, and tests

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

app/modules/core/services/menu_service.py

@@ -325,6 +325,106 @@ class MenuService:
 
         return all_enabled
 
+    def get_merchant_primary_platform_id(
+        self,
+        db: Session,
+        merchant_id: int,
+    ) -> int | None:
+        """
+        Get the primary platform ID for a merchant's visibility config.
+
+        Resolution order:
+        1. Platform from the store marked is_primary in StorePlatform
+        2. First active subscription's platform (fallback)
+
+        Args:
+            db: Database session
+            merchant_id: Merchant ID
+
+        Returns:
+            Platform ID or None if no active subscriptions
+        """
+        from app.modules.billing.models.merchant_subscription import (
+            MerchantSubscription,
+        )
+        from app.modules.billing.models.subscription import SubscriptionStatus
+        from app.modules.tenancy.models import Store
+        from app.modules.tenancy.models.store_platform import StorePlatform
+
+        active_statuses = [
+            SubscriptionStatus.TRIAL.value,
+            SubscriptionStatus.ACTIVE.value,
+            SubscriptionStatus.PAST_DUE.value,
+            SubscriptionStatus.CANCELLED.value,
+        ]
+
+        # Try to find the primary store's platform
+        primary_platform_id = (
+            db.query(StorePlatform.platform_id)
+            .join(Store, Store.id == StorePlatform.store_id)
+            .join(
+                MerchantSubscription,
+                (MerchantSubscription.platform_id == StorePlatform.platform_id)
+                & (MerchantSubscription.merchant_id == merchant_id),
+            )
+            .filter(
+                Store.merchant_id == merchant_id,
+                Store.is_active == True,  # noqa: E712
+                StorePlatform.is_primary == True,  # noqa: E712
+                StorePlatform.is_active == True,  # noqa: E712
+                MerchantSubscription.status.in_(active_statuses),
+            )
+            .first()
+        )
+
+        if primary_platform_id:
+            return primary_platform_id[0]
+
+        # Fallback: first active subscription's platform
+        first_sub = (
+            db.query(MerchantSubscription.platform_id)
+            .filter(
+                MerchantSubscription.merchant_id == merchant_id,
+                MerchantSubscription.status.in_(active_statuses),
+            )
+            .order_by(MerchantSubscription.id)
+            .first()
+        )
+
+        return first_sub[0] if first_sub else None
+
+    def get_store_primary_platform_id(
+        self,
+        db: Session,
+        store_id: int,
+    ) -> int | None:
+        """
+        Get the primary platform ID for a store's menu visibility config.
+
+        Prefers the active StorePlatform marked is_primary, falls back to
+        the first active StorePlatform by ID.
+
+        Args:
+            db: Database session
+            store_id: Store ID
+
+        Returns:
+            Platform ID or None if no active store-platform link
+        """
+        from app.modules.tenancy.models.store_platform import StorePlatform
+
+        sp = (
+            db.query(StorePlatform.platform_id)
+            .filter(
+                StorePlatform.store_id == store_id,
+                StorePlatform.is_active == True,  # noqa: E712
+            )
+            .order_by(StorePlatform.is_primary.desc(), StorePlatform.id)
+            .first()
+        )
+
+        return sp[0] if sp else None
+
     def get_merchant_for_menu(
         self,
         db: Session,