Fix: Use simple HTML output to test routing

- Changed AdminController to use simple echo/exit instead of TemplateResponse
  - Eliminates TemplateResponse complexity
  - Direct HTML output for debugging
- Simplified routes.php to single admin route
  - Removed test route (no longer needed)
  - Simple GET only route
- Simplified Application.php
  - Removed resource loading
  - Minimal bootstrap

If this shows 'Controller is working' page, routing is confirmed working.
If it still redirects to dashboard, it's a Nextcloud routing issue.

This is a minimal test version to confirm routing works before building full UI.

analyticshub/appinfo/routes.php

@@ -4,23 +4,13 @@ declare(strict_types=1);
 
 namespace OCA\AnalyticsHub;
 
-use OCP\AppFramework\Http\TemplateResponse;
-use OCP\AppFramework\Http\JSONResponse;
-
 /**
  * Routes for Mini-CMO Analytics Hub
  */
 
 return [
     'routes' => [
-        // Test route
-        [
-            'name' => 'admin#test',
-            'url' => '/test',
-            'verb' => 'GET',
-            'requirements' => [],
-        ],
-        // Admin routes
+        // Admin route - simple GET only
         [
             'name' => 'admin#index',
             'url' => '/admin',