feat:實作 API 效能優化 — Redis 快取、分頁、DB 索引

- 引入 Redis（predis）快取層：Admin Stats（5分鐘）、課程列表（3分鐘，tag-based 失效）、評價分布（10分鐘）
- ReviewController::publicList 改為 paginate + eager load votes，消除 N+1
- AdminReviewController::index 加入分頁（預設 20，最大 100）
- 新增 notifications / diving_offers 效能索引 migration
- 新增 docker-compose.override.yml 本機開發 port mapping 機制（不進 git）

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

app/Http/Controllers/API/AdminStatsController.php

@@ -5,6 +5,7 @@ namespace App\Http\Controllers\API;
 use App\Http\Controllers\Controller;
 use App\Models\DivingOffer;
 use App\Models\User;
+use Illuminate\Support\Facades\Cache;
 
 class AdminStatsController extends Controller
 {
@@ -14,13 +15,12 @@ class AdminStatsController extends Controller
             return response()->json(['status' => false, 'message' => '無權限存取'], 403);
         }
 
-        return response()->json([
-            'status' => true,
-            'data'   => [
-                'total_members'   => User::where('role', 'member')->count(),
-                'total_providers' => User::where('role', 'provider')->count(),
-                'total_offers'    => DivingOffer::count(),
-            ],
+        $stats = Cache::remember('admin_stats', 300, fn() => [
+            'total_members'   => User::where('role', 'member')->count(),
+            'total_providers' => User::where('role', 'provider')->count(),
+            'total_offers'    => DivingOffer::count(),
         ]);
+
+        return response()->json(['status' => true, 'data' => $stats]);
     }
 }