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

IT_asset_management/config.py

@@ -54,6 +54,9 @@ class Config:
     PORTAL_LOGIN_URL = os.environ.get('PORTAL_LOGIN_URL', 'http://localhost:8080/login')
     PORTAL_LOGOUT_URL = os.environ.get('PORTAL_LOGOUT_URL', 'http://localhost:8080/logout')
 
+    # Internal service-to-service sync secret — must match portal's INTERNAL_SYNC_SECRET
+    INTERNAL_SYNC_SECRET = os.environ.get('INTERNAL_SYNC_SECRET', 'change-this-internal-secret')
+
     # Pagination
     ITEMS_PER_PAGE = int(os.environ.get('ITEMS_PER_PAGE', 25))