Fix: Add proper Application.php and fix DI

- Created appinfo/Application.php (Nextcloud app bootstrap)
  - Extends OCP\AppFramework\App
  - Registers proper app ID: analyticshub
  - Loads CSS and JS files
- Removed obsolete lib/App.php file
- Updated all AppInfo::APP_NAME references to Application::APP_NAME
  - AdminController, ApiV1Controller
  - GoogleAnalyticsService, LLMService
- Fixed dependency injection in AdminController
  - Injected IConfig service properly
- Added missing use statements

This is the core fix for the app not appearing in Nextcloud.
Nextcloud requires appinfo/Application.php to initialize the app.

analyticshub/lib/Controller/ApiV1Controller.php

@@ -9,6 +9,7 @@ use OCP\IResponse;
 use OCP\AppFramework\Http;
 use OCP\AppFramework\Http\DataResponse;
 use OCP\AppFramework\Http\JSONResponse;
+use OCA\AnalyticsHub\AppInfo\Application;
 
 use OCA\AnalyticsHub\Service\GoogleAnalyticsService;
 use OCA\AnalyticsHub\Service\LLMService;
@@ -146,7 +147,7 @@ class ApiV1Controller {
         $this->validateAgentAccess();
 
         $status = [
-            'app_name' => AppInfo::APP_NAME,
+            'app_name' => Application::APP_NAME,
             'version' => AppInfo::getVersion(),
             'status' => 'operational',
             'google_analytics' => $this->gaService->isConfigured() ? 'configured' : 'not_configured',