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/appinfo/Application.php

@@ -0,0 +1,25 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OCA\AnalyticsHub\AppInfo;
+
+use OCP\AppFramework\App;
+use OCP\Util;
+
+/**
+ * Application class for Mini-CMO Analytics Hub
+ */
+class Application extends App {
+
+    public const APP_NAME = 'analyticshub';
+    public const APP_ID = 'analyticshub';
+
+    public function __construct(array $urlParams = []) {
+        parent::__construct(self::APP_ID, $urlParams);
+
+        // Load scripts and styles
+        Util::addStyle(self::APP_ID, 'admin');
+        Util::addScript(self::APP_ID, 'admin');
+    }
+}