feat(profile): add uploadable avatars with local/S3 storage

Users can upload and remove profile pictures on the profile page.
Admins choose local or instance S3 storage in advanced settings.
Avatars are compressed to JPEG and served via a private cached route.

app/Http/Controllers/ProfileAvatarController.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace App\Http\Controllers;
+
+use App\Services\AvatarStorageService;
+use Illuminate\Http\Response;
+
+class ProfileAvatarController extends Controller
+{
+    public function __invoke(AvatarStorageService $avatarStorage): Response
+    {
+        $contents = $avatarStorage->contents(auth()->user());
+        abort_if($contents === null, 404);
+
+        return response($contents, 200, [
+            'Content-Type' => 'image/jpeg',
+            'Cache-Control' => 'private, max-age=300',
+        ]);
+    }
+}