feat: RBAC Phase 1 — consolidate user roles into 4-value enum

Consolidate User.role (2-value: admin/store) + User.is_super_admin (boolean)
into a single 4-value UserRole enum: super_admin, platform_admin,
merchant_owner, store_member. Drop stale StoreUser.user_type column.
Fix role="user" bug in merchant creation.

Key changes:
- Expand UserRole enum from 2 to 4 values with computed properties
  (is_admin, is_super_admin, is_platform_admin, is_merchant_owner, is_store_user)
- Add Alembic migration (tenancy_003) for data migration + column drops
- Remove is_super_admin from JWT token payload
- Update all auth dependencies, services, routes, templates, JS, and tests
- Update all RBAC documentation

66 files changed, 1219 unit tests passing.

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

tests/fixtures/store_fixtures.py

@@ -70,7 +70,7 @@ def test_store(db, test_merchant):
 @pytest.fixture
 def test_store_with_store_user(db, test_store_user):
     """Create a store owned by a store user (for testing store API endpoints)."""
-    from app.modules.tenancy.models import StoreUser, StoreUserType
+    from app.modules.tenancy.models import StoreUser
 
     unique_id = str(uuid.uuid4())[:8].upper()
 
@@ -98,11 +98,10 @@ def test_store_with_store_user(db, test_store_user):
     db.commit()
     db.refresh(store)
 
-    # Create StoreUser association
+    # Create StoreUser association (ownership determined via Merchant.owner_user_id)
     store_user = StoreUser(
         store_id=store.id,
         user_id=test_store_user.id,
-        user_type=StoreUserType.OWNER.value,
         is_active=True,
     )
     db.add(store_user)