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/GuestbookController.php

@@ -8,11 +8,12 @@ use App\Http\Controllers\Controller;
 use App\Http\Requests\GuestbookFormRequest;
 use App\Models\User;
 use App\Models\User\WebsiteUserGuestbook;
+use Illuminate\Http\RedirectResponse;
 use Illuminate\Support\Facades\Auth;
 
 class GuestbookController extends Controller
 {
-    public function store(User $user, GuestbookFormRequest $request)
+    public function store(User $user, GuestbookFormRequest $request): RedirectResponse
     {
         $this->validateGuestbookPost($user, $request);
 
@@ -24,7 +25,7 @@ class GuestbookController extends Controller
         return redirect()->back()->with('success', __('Your message has been posted.'));
     }
 
-    public function destroy(User $user, WebsiteUserGuestbook $guestbook)
+    public function destroy(User $user, WebsiteUserGuestbook $guestbook): RedirectResponse
     {
         if ($guestbook->user_id !== Auth::id() && $guestbook->profile_id !== $user->id && Auth::user()->rank < (int) setting('min_staff_rank')) {
             return redirect()->back()->withErrors([
@@ -37,7 +38,7 @@ class GuestbookController extends Controller
         return redirect()->back()->with('success', __('Your message has been deleted.'));
     }
 
-    private function validateGuestbookPost(User $user, GuestbookFormRequest $request)
+    private function validateGuestbookPost(User $user, GuestbookFormRequest $request): ?RedirectResponse
     {
         if ($user->id === $request->user()->id) {
             return $this->redirectWithError(__('You cannot post a message on your own profile.'));
@@ -49,7 +50,7 @@ class GuestbookController extends Controller
         }
     }
 
-    private function redirectWithError($message)
+    private function redirectWithError(string $message): RedirectResponse
     {
         return redirect()->back()->withErrors(['message' => $message]);
     }