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>

routes/web.php

@@ -1,5 +1,7 @@
 <?php
 
+use App\Http\Controllers\CompareController;
+use App\Http\Controllers\GameCommentController;
 use App\Http\Controllers\GameController;
 use App\Http\Controllers\HomeController;
 use App\Http\Controllers\LibraryController;
@@ -21,6 +23,11 @@ Route::get('/games/{game:slug}', [GameController::class, 'show'])->name('games.s
 Route::get('/users/{user:username}', [UserController::class, 'show'])->name('users.show');
 Route::get('/users/{user:username}/library', [UserController::class, 'library'])->name('users.library');
 
+// Compare (auth required)
+Route::middleware('auth')->group(function () {
+    Route::get('/users/{user:username}/compare', [CompareController::class, 'show'])->name('users.compare');
+});
+
 // Library (auth required)
 Route::middleware('auth')->group(function () {
     Route::post('/library', [LibraryController::class, 'store'])->name('library.store');
@@ -35,6 +42,12 @@ Route::middleware('auth')->group(function () {
     Route::delete('/reviews/{review}', [\App\Http\Controllers\ReviewController::class, 'destroy'])->name('reviews.destroy');
 });
 
+// Comments (auth required)
+Route::middleware('auth')->group(function () {
+    Route::post('/games/{game:slug}/comments', [GameCommentController::class, 'store'])->name('games.comments.store');
+    Route::delete('/comments/{comment}', [GameCommentController::class, 'destroy'])->name('comments.destroy');
+});
+
 // Lists
 Route::get('/lists', [\App\Http\Controllers\ListController::class, 'index'])->name('lists.index')->middleware('auth');
 Route::post('/lists', [\App\Http\Controllers\ListController::class, 'store'])->name('lists.store')->middleware('auth');