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>

app/modules/analytics/services/stats_service.py

@@ -420,7 +420,7 @@ class StatsService:
             total_users = db.query(User).count()
             active_users = db.query(User).filter(User.is_active == True).count()
             inactive_users = total_users - active_users
-            admin_users = db.query(User).filter(User.role == "admin").count()
+            admin_users = db.query(User).filter(User.role.in_(["super_admin", "platform_admin"])).count()
 
             return {
                 "total_users": total_users,