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/tenancy/static/admin/js/admin-user-detail.js

@@ -86,7 +86,7 @@ function adminUserDetailPage() {
                 adminUserDetailLog.info(`Admin user loaded in ${duration}ms`, {
                     id: this.adminUser.id,
                     username: this.adminUser.username,
-                    is_super_admin: this.adminUser.is_super_admin,
+                    role: this.adminUser.role,
                     is_active: this.adminUser.is_active
                 });
                 adminUserDetailLog.debug('Full admin user data:', this.adminUser);