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/User/UserReferralController.php

@@ -4,10 +4,11 @@ namespace App\Http\Controllers\User;
 
 use App\Http\Controllers\Controller;
 use App\Models\User;
+use Illuminate\View\View;
 
 class UserReferralController extends Controller
 {
-    public function __invoke(string $referralCode)
+    public function __invoke(string $referralCode): View
     {
         if (! User::where('referral_code', $referralCode)->exists()) {
             abort(404);