Fix: Simplify integration and fix admin template

- Removed settings/navigation from appinfo/info.xml
  - These sections can cause routing conflicts
  - App now relies purely on routes.php
- Simplified Application.php
  - Removed manual service/controller registration
  - Let Nextcloud DI framework handle it automatically
- Fixed admin template to use Nextcloud standards
  - Removed non-standard style() call
  - Added proper l10n support with p($l->t(...))
  - Clean template structure
- Created css/admin.css
  - Nextcloud-compatible styling
  - Matches design language
- Created js/admin.js
  - Handles Save Configuration button
  - Handles Test Connection button
  - Uses OC, OC.Notification APIs

This should fix admin page not appearing issue.
Users can access via: Settings → Administration → Additional Settings

analyticshub/appinfo/info.xml

@@ -24,15 +24,4 @@
     <nextcloud min-version="25" max-version="26"/>
     <php min-version="7.4"/>
   </dependencies>
-  <settings>
-    <admin>OCA\AnalyticsHub\Controller\Admin</admin>
-  </settings>
-  <navigation>
-    <admin>analyticshub.admin.index</admin>
-  </navigation>
-  <repair-steps>
-  <step>Repair steps not needed</step>
-  <repair-step>Or remove and reinstall</repair-step>
-  <repair-step>Check Nextcloud logs for errors</repair-step>
-  </repair-steps>
 </info>