feat: upload wizard refactor + vision AI tags + artwork versioning

Upload wizard:
- Refactored UploadWizard into modular steps (Step1FileUpload, Step2Details, Step3Publish)
- Extracted reusable hooks: useUploadMachine, useFileValidation, useVisionTags
- Extracted reusable components: CategorySelector, ContentTypeSelector
- Added TagPicker component (studio-style list picker with AI badge + new-tag insertion)
- Fixed TagInput auto-open bug (hasFocusedRef guard)
- Replaced TagInput with TagPicker in UploadSidebar

Vision AI tag suggestions:
- Add UploadVisionSuggestController: sync POST /api/uploads/{id}/vision-suggest
- Calls vision.klevze.net/analyze/all on upload completion (before step 2 opens)
- Two-phase useVisionTags: immediate gateway call + background DB polling
- Trigger fires on uploadReady (not step change) so tags arrive before user sees step 2
- Added vision.gateway config block with VISION_GATEWAY_URL env

Artwork versioning system:
- ArtworkVersion / ArtworkVersionEvent models
- ArtworkVersioningService: createNewVersion, restoreVersion, rate limiting, ranking decay
- Migrations: artwork_versions, artwork_version_events, versioning columns on artworks
- Studio API routes: GET versions, POST restore/{version_id}
- Feature tests: ArtworkVersioningTest (13 cases)

config/cdn.php

@@ -3,6 +3,15 @@
 declare(strict_types=1);
 
 return [
-    'files_url' => env('FILES_CDN_URL', 'https://files.skinbase.org'),
+    'files_url'  => env('FILES_CDN_URL',  'https://files.skinbase.org'),
     'avatar_url' => env('AVATAR_CDN_URL', 'https://files.skinbase.org'),
+
+    /**
+     * Optional CDN purge webhook URL.
+     * When set, the artwork versioning system will POST { paths: [...] }
+     * after every file replacement to bust stale thumbnails.
+     *
+     * Example: https://api.cloudflare.com/client/v4/zones/{zone_id}/purge_cache
+     */
+    'purge_url'  => env('CDN_PURGE_URL', null),
 ];