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/PostReactionController.php

@@ -0,0 +1,75 @@
+<?php
+
+namespace App\Http\Controllers\Api\Posts;
+
+use App\Http\Controllers\Controller;
+use App\Models\Post;
+use App\Models\PostReaction;
+use App\Services\Posts\PostCountersService;
+use Illuminate\Http\JsonResponse;
+use Illuminate\Http\Request;
+use Illuminate\Support\Facades\RateLimiter;
+
+class PostReactionController extends Controller
+{
+    public function __construct(private PostCountersService $counters) {}
+
+    /**
+     * POST /api/posts/{id}/reactions
+     * payload: { reaction: 'like' }
+     */
+    public function store(Request $request, int $id): JsonResponse
+    {
+        $user = $request->user();
+
+        $key = 'react_post:' . $user->id;
+        if (RateLimiter::tooManyAttempts($key, 60)) {
+            return response()->json(['message' => 'Too many reactions. Please slow down.'], 429);
+        }
+        RateLimiter::hit($key, 3600);
+
+        $post     = Post::findOrFail($id);
+        $reaction = $request->input('reaction', 'like');
+
+        $existing = PostReaction::where('post_id', $post->id)
+            ->where('user_id', $user->id)
+            ->where('reaction', $reaction)
+            ->first();
+
+        if ($existing) {
+            return response()->json(['message' => 'Already reacted.', 'reactions_count' => $post->reactions_count], 200);
+        }
+
+        PostReaction::create([
+            'post_id'  => $post->id,
+            'user_id'  => $user->id,
+            'reaction' => $reaction,
+        ]);
+
+        $this->counters->incrementReactions($post);
+        $post->refresh();
+
+        return response()->json(['reactions_count' => $post->reactions_count, 'viewer_liked' => true], 201);
+    }
+
+    /**
+     * DELETE /api/posts/{id}/reactions/{reaction}
+     */
+    public function destroy(Request $request, int $id, string $reaction = 'like'): JsonResponse
+    {
+        $user = $request->user();
+        $post = Post::findOrFail($id);
+
+        $deleted = PostReaction::where('post_id', $post->id)
+            ->where('user_id', $user->id)
+            ->where('reaction', $reaction)
+            ->delete();
+
+        if ($deleted) {
+            $this->counters->decrementReactions($post);
+            $post->refresh();
+        }
+
+        return response()->json(['reactions_count' => $post->reactions_count, 'viewer_liked' => false]);
+    }
+}