IT Assets: add role-based auth system and portal user sync

Auth:
- Fix local login (was redirecting to portal; now authenticates AdminUser directly)
- Portal SSO still takes priority in production via nginx headers

Role system (admin | editor | readonly):
- New app/utils/decorators.py with editor_required and admin_required decorators
- All write routes protected with editor_required (create/edit/delete/import/mask)
- Settings user management protected with admin_required
- Sidebar hides write-only links for readonly users
- Dashboard quick actions and list page buttons hidden for readonly

Settings page:
- Role colour badges (admin=red, editor=blue, readonly=grey)
- Inline role changer per user (dropdown auto-submit)
- Reset password modal per user
- Delete user button with confirmation
- Add user form includes role selector with legend

Portal user sync:
- New /internal/sync-user endpoint receives user pre-creation from portal
- INTERNAL_SYNC_SECRET added to config
- portal/config.py: added internal_url for itassets app so _sync_user_to_app works

portal/config.py

@@ -46,6 +46,8 @@ class Config:
             'icon': '💼',
             'url': '/itassets/',
             'color': '#f59e0b',
+            # Internal URL for portal→app user sync (not through nginx)
+            'internal_url': os.environ.get('ITASSETS_INTERNAL_URL', 'http://localhost:5003'),
         },
         {
             'id': 'srvmonitor',