refactor: add return type hints to all controller methods

Added proper return types (View, RedirectResponse, JsonResponse, Collection)
to 40+ controller methods across 16 controllers. Also added missing
imports for Illuminate response types and tightened parameter types
(e.g. InstallationController::showStep now uses int instead of mixed).

app/Http/Controllers/Help/HelpCenterController.php

@@ -5,10 +5,11 @@ namespace App\Http\Controllers\Help;
 use App\Http\Controllers\Controller;
 use App\Models\Help\WebsiteHelpCenterCategory;
 use Illuminate\Support\Facades\Cache;
+use Illuminate\View\View;
 
 class HelpCenterController extends Controller
 {
-    public function __invoke()
+    public function __invoke(): View
     {
         $categories = Cache::remember('help_center_categories', 300, fn () => WebsiteHelpCenterCategory::orderBy('position')->get());