feat: registration field polish, multi-category tags, file uploads, Partner icon

- Restructure field editor dialog: move Options section to bottom with
  divider and subheader, fix delete button with flex layout
- Change tag_category (single string) to tag_categories (JSON array)
  supporting multiple category selection in tag picker fields
- Portal tag picker now groups tags by category with subheaders
- Add generic file upload endpoint (FileUploadService + UploadController)
- Replace email branding logo URL text field with ImageUploadField
- Update Partner crowd type default icon to tabler-affiliate
- Apply changes consistently to both field and template dialogs

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/app/Services/FileUploadService.php

@@ -0,0 +1,67 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Services;
+
+use Illuminate\Http\UploadedFile;
+use Illuminate\Support\Facades\Storage;
+use Illuminate\Support\Str;
+
+final class FileUploadService
+{
+    private const ALLOWED_IMAGE_MIMES = [
+        'image/jpeg',
+        'image/png',
+        'image/webp',
+        'image/svg+xml',
+        'image/gif',
+    ];
+
+    private const MAX_IMAGE_SIZE_KB = 5120; // 5MB
+
+    public function uploadImage(
+        UploadedFile $file,
+        string $directory,
+        ?string $organisationId = null,
+    ): string {
+        $this->validateImage($file);
+
+        $extension = $file->getClientOriginalExtension();
+        $filename = Str::ulid() . '.' . $extension;
+        $path = trim($directory, '/');
+
+        if ($organisationId) {
+            $path .= '/' . $organisationId;
+        }
+
+        Storage::disk('public')->putFileAs($path, $file, $filename);
+
+        return Storage::disk('public')->url($path . '/' . $filename);
+    }
+
+    public function deleteByUrl(string $url): void
+    {
+        $baseUrl = Storage::disk('public')->url('');
+        $path = str_replace($baseUrl, '', $url);
+
+        if ($path && Storage::disk('public')->exists($path)) {
+            Storage::disk('public')->delete($path);
+        }
+    }
+
+    private function validateImage(UploadedFile $file): void
+    {
+        if (!in_array($file->getMimeType(), self::ALLOWED_IMAGE_MIMES, true)) {
+            throw new \DomainException(
+                'Alleen JPG, PNG, WebP, SVG of GIF bestanden zijn toegestaan.'
+            );
+        }
+
+        if ($file->getSize() / 1024 > self::MAX_IMAGE_SIZE_KB) {
+            throw new \DomainException(
+                'Bestand is te groot. Maximum: 5MB.'
+            );
+        }
+    }
+}