feat: loyalty feature provider, admin data fixes, storefront mobile menu

- Add LoyaltyFeatureProvider with 11 BINARY/MERCHANT features for billing
  feature gating, wired into loyalty module definition
- Fix subscription-tiers admin page showing 0 features by populating
  feature_codes from tier relationship in all admin tier endpoints
- Fix merchants admin page showing 0 stores and N/A owner by adding
  store_count and owner_email to MerchantResponse and eager-loading owner
- Add "no tiers" warning with link in subscription creation modal when
  platform has no configured tiers
- Add missing mobile menu panel to storefront base template so hamburger
  toggle actually shows navigation links

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

app/modules/tenancy/routes/api/admin_merchants.py

@@ -109,6 +109,7 @@ def get_all_merchants(
                 name=c.name,
                 description=c.description,
                 owner_user_id=c.owner_user_id,
+                owner_email=c.owner.email if c.owner else None,
                 contact_email=c.contact_email,
                 contact_phone=c.contact_phone,
                 website=c.website,
@@ -118,6 +119,7 @@ def get_all_merchants(
                 is_verified=c.is_verified,
                 created_at=c.created_at.isoformat(),
                 updated_at=c.updated_at.isoformat(),
+                store_count=c.store_count,
             )
             for c in merchants
         ],