fix(astrolabe): Fix NcSelect options and CSS loading

- Use :input-label prop for NcSelect field labels instead of :label
  (the :label prop sets the option label property key, not the visible label)
- Fix CSS loading in admin.php and personal.php templates to use
  astrolabe-main (the bundled CSS file)
- Update minimum Nextcloud version to 31 (required for Vue 3)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

third_party/astrolabe/templates/settings/admin.php

@@ -7,7 +7,7 @@
  */
 
 script('astrolabe', 'astrolabe-adminSettings');
-style('astrolabe', 'astrolabe-adminSettings');
+style('astrolabe', 'astrolabe-main');  // All CSS bundled into main
 ?>
 
 <div id="astrolabe-admin-settings" class="section">