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

app/Providers/AppServiceProvider.php

@@ -65,6 +65,16 @@ class AppServiceProvider extends ServiceProvider
         ArtworkComment::observe(ArtworkCommentObserver::class);
         ArtworkReaction::observe(ArtworkReactionObserver::class);
 
+        // ── Posts / Feed System Events ──────────────────────────────────────
+        Event::listen(
+            \App\Events\Posts\ArtworkShared::class,
+            \App\Listeners\Posts\SendArtworkSharedNotification::class,
+        );
+        Event::listen(
+            \App\Events\Posts\PostCommented::class,
+            \App\Listeners\Posts\SendPostCommentedNotification::class,
+        );
+
         // Provide toolbar counts and user info to layout views (port of legacy toolbar logic)
         View::composer(['layouts.nova', 'layouts.nova.*'], function ($view) {
             $uploadCount = $favCount = $msgCount = $noticeCount = 0;