Add friend library comparison and game comments features

- CompareController: side-by-side library diff with stats (common games, rating diff)
- GameCommentController + GameCommentPolicy: threaded comments with replies, auth-gated
- GameComment model with top-level scope and self-referential replies relation
- Migration: game_comments table with parent_id for threading
- games/show: Discussion section with Alpine.js (post, reply, delete)
- compare/show: tabbed view (in common, they have, you have) with game cards
- users/show: "Compare Libraries" button visible to other authenticated users

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/Http/Controllers/GameController.php

@@ -3,6 +3,7 @@
 namespace App\Http\Controllers;
 
 use App\Models\Game;
+use App\Models\GameComment;
 use App\Models\Genre;
 use App\Models\Platform;
 use Illuminate\Http\Request;
@@ -54,7 +55,13 @@ class GameController extends Controller
             $userLists  = auth()->user()->lists()->get(['id', 'title']);
         }
 
-        $response = view('games.show', compact('game', 'userGame', 'userReview', 'userLists'));
+        $comments = $game->comments()->whereNull('parent_id')
+            ->with(['user', 'replies.user'])
+            ->latest()
+            ->limit(20)
+            ->get();
+
+        $response = view('games.show', compact('game', 'userGame', 'userReview', 'userLists', 'comments'));
         return auth()->check()
             ? $response
             : response($response)->header('Cache-Control', 'public, max-age=300');