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/database/seeders/DevSeeder.php

@@ -124,7 +124,7 @@ class DevSeeder extends Seeder
                 ['name' => 'Pers', 'system_type' => 'PRESS', 'color' => '#FF9800', 'icon' => 'tabler-camera'],
                 ['name' => 'Gast', 'system_type' => 'GUEST', 'color' => '#607D8B', 'icon' => 'tabler-ticket'],
                 ['name' => 'Leverancier', 'system_type' => 'SUPPLIER', 'color' => '#795548', 'icon' => 'tabler-truck-delivery'],
-                ['name' => 'Partner', 'system_type' => 'PARTNER', 'color' => '#FFC107', 'icon' => 'tabler-handshake'],
+                ['name' => 'Partner', 'system_type' => 'PARTNER', 'color' => '#FFC107', 'icon' => 'tabler-affiliate'],
             ];
 
             foreach ($crowdTypesData as $data) {