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/Http/Controllers/Api/Posts/PostCommentHighlightController.php

@@ -0,0 +1,55 @@
+<?php
+
+namespace App\Http\Controllers\Api\Posts;
+
+use App\Http\Controllers\Controller;
+use App\Models\Post;
+use App\Models\PostComment;
+use Illuminate\Http\JsonResponse;
+use Illuminate\Http\Request;
+use Illuminate\Support\Facades\DB;
+
+/**
+ * POST   /api/posts/{post_id}/comments/{comment_id}/highlight
+ * DELETE /api/posts/{post_id}/comments/{comment_id}/highlight
+ *
+ * Only the post owner may highlight/un-highlight.
+ * Only 1 highlighted comment per post is allowed at a time.
+ */
+class PostCommentHighlightController extends Controller
+{
+    public function highlight(Request $request, int $postId, int $commentId): JsonResponse
+    {
+        $post    = Post::findOrFail($postId);
+        $comment = PostComment::where('post_id', $postId)->findOrFail($commentId);
+
+        if ($request->user()->id !== $post->user_id) {
+            abort(403, 'Only the post owner can highlight comments.');
+        }
+
+        DB::transaction(function () use ($post, $comment) {
+            // Remove any existing highlight on this post
+            PostComment::where('post_id', $post->id)
+                ->where('is_highlighted', true)
+                ->update(['is_highlighted' => false]);
+
+            $comment->update(['is_highlighted' => true]);
+        });
+
+        return response()->json(['message' => 'Comment highlighted.', 'comment_id' => $comment->id]);
+    }
+
+    public function unhighlight(Request $request, int $postId, int $commentId): JsonResponse
+    {
+        $post    = Post::findOrFail($postId);
+        $comment = PostComment::where('post_id', $postId)->findOrFail($commentId);
+
+        if ($request->user()->id !== $post->user_id) {
+            abort(403, 'Only the post owner can remove comment highlights.');
+        }
+
+        $comment->update(['is_highlighted' => false]);
+
+        return response()->json(['message' => 'Highlight removed.', 'comment_id' => $comment->id]);
+    }
+}