fix: use /enabled endpoint instead of app_api's ocs state check

[kyteinsky]

enabled state is inconsistent between app_api and the ex-app during initial setup.

The enabled flag in app_api is written to the DB before /init is called (i.e., before model download begins), while the ex-app's own /enabled endpoint is called only after /init completes. As a result, during the initial installation phase:

• Calls routed through the ex-app work correctly (it reports its true state).
• Direct checks against app_api's internal state (with nc.enabled_state, which hits /ocs/v1.php/apps/app_api/ex-app/state) can return a stale/incorrect enabled value.

This is a race condition limited to only the app registration/installation part, once /init finishes, both sources report the same.

🤖 AI (if applicable)

• The content of this PR was partly or fully generated using AI (N/A)

[marcelklehr]

fingers crossed this won't break things