feat(astrolabe): implement app password provisioning for multi-user background sync

Adds complete app password provisioning workflow for multi-user BasicAuth
deployments, allowing users to independently enable background sync by
generating and storing Nextcloud app passwords.

**New Components:**

Backend (PHP):
- CredentialsController: Validates and stores app passwords
  * Validates app password format and authenticity via OCS API
  * Stores encrypted passwords in oc_preferences
  * Provides status and credential management endpoints
- AstrolabeAdminSettings: Admin configuration page for MCP server URL
- AstrolabeAdminSettingsListener: Event listener for admin section
- Updated McpTokenStorage: Added background sync credential methods

Frontend:
- personalSettings.js: Form handling for app password entry
  * AJAX submission with error handling
  * Shows success/error notifications
  * Triggers page reload after successful save
- settings.css: Styling for settings pages
- Updated personal.php template: Two-option UI
  * Option 1: OAuth refresh token (future, not yet available)
  * Option 2: App password (works today, recommended)
  * Shows "Active" badge when provisioned
  * Displays credential type and provisioned timestamp

Routes:
- POST /api/v1/background-sync/credentials - Store app password
- GET /api/v1/background-sync/status - Get provisioning status
- DELETE /api/v1/background-sync/credentials - Revoke credentials
- GET /api/v1/background-sync/credentials/{userId} - Admin only

**Testing:**
- test_astrolabe_settings_buttons.py: Integration test for UI buttons

**Workflow:**
1. User generates app password in Nextcloud Security settings
2. User navigates to Astrolabe personal settings
3. User enters app password in "Option 2: App Password" form
4. Backend validates password via OCS API call
5. Password stored encrypted in oc_preferences
6. Page reloads showing "Active" badge with credential details
7. MCP server can now use stored password for background operations

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

third_party/astrolabe/lib/AppInfo/Application.php

@@ -4,11 +4,15 @@ declare(strict_types=1);
 
 namespace OCA\Astrolabe\AppInfo;
 
+use OCA\Astrolabe\Listener\AstrolabeAdminSettingsListener;
 use OCA\Astrolabe\Search\SemanticSearchProvider;
+use OCA\Astrolabe\Settings\AstrolabeAdminSettings;
 use OCP\AppFramework\App;
 use OCP\AppFramework\Bootstrap\IBootContext;
 use OCP\AppFramework\Bootstrap\IBootstrap;
 use OCP\AppFramework\Bootstrap\IRegistrationContext;
+use OCP\Settings\Events\DeclarativeSettingsGetValueEvent;
+use OCP\Settings\Events\DeclarativeSettingsSetValueEvent;
 
 class Application extends App implements IBootstrap {
 	public const APP_ID = 'astrolabe';
@@ -21,6 +25,19 @@ class Application extends App implements IBootstrap {
 	public function register(IRegistrationContext $context): void {
 		// Register unified search provider for semantic search
 		$context->registerSearchProvider(SemanticSearchProvider::class);
+
+		// Register declarative admin settings
+		$context->registerDeclarativeSettings(AstrolabeAdminSettings::class);
+
+		// Register event listeners for declarative settings
+		$context->registerEventListener(
+			DeclarativeSettingsGetValueEvent::class,
+			AstrolabeAdminSettingsListener::class
+		);
+		$context->registerEventListener(
+			DeclarativeSettingsSetValueEvent::class,
+			AstrolabeAdminSettingsListener::class
+		);
 	}
 
 	public function boot(IBootContext $context): void {