feat: forum rich-text editor, emoji picker, mentions, discover nav, feed, uploads, profile

Forum:
- TipTap WYSIWYG editor with full toolbar
- @emoji-mart/react emoji picker (consistent with tweets)
- @mention autocomplete with user search API
- Fix PHP 8.4 parse errors in Blade templates
- Fix thread data display (paginator items)
- Align forum page widths to max-w-5xl

Discover:
- Extract shared _nav.blade.php partial
- Add missing nav links to for-you page
- Add Following link for authenticated users

Feed/Posts:
- Post model, controllers, policies, migrations
- Feed page components (PostComposer, FeedCard, etc)
- Post reactions, comments, saves, reports, sharing
- Scheduled publishing support
- Link preview controller

Profile:
- Profile page components (ProfileHero, ProfileTabs)
- Profile API controller

Uploads:
- Upload wizard enhancements
- Scheduled publish picker
- Studio status bar and readiness checklist

config/uploads.php

@@ -6,14 +6,16 @@ return [
     'storage_root' => env('SKINBASE_STORAGE_ROOT', storage_path('app/artworks')),
 
     'paths' => [
-        'tmp' => 'tmp',
+        'tmp'      => 'tmp',
         'quarantine' => 'quarantine',
-        'originals' => 'originals',
-        'public' => 'public',
+        'original' => 'original',
+        'xs'       => 'xs',
+        'sm'       => 'sm',
+        'md'       => 'md',
+        'lg'       => 'lg',
+        'xl'       => 'xl',
     ],
 
-    'public_img_prefix' => 'img',
-
     'max_size_mb' => 50,
     'max_pixels' => 12000,
 
@@ -26,8 +28,8 @@ return [
     'allow_gif' => env('UPLOAD_ALLOW_GIF', false),
 
     'derivatives' => [
-        'thumb' => ['max' => 320],
-        'sq' => ['size' => 512],
+        'xs' => ['max' => 320],
+        'sm' => ['max' => 680],
         'md' => ['max' => 1024],
         'lg' => ['max' => 1920],
         'xl' => ['max' => 2560],