feat:實作通知系統 — 站內通知、Email 通知、Polling 機制

後端
- 新增 6 個 Notification class（預約建立/確認/拒絕/取消/完成、收到評價），database + mail 雙 channel
- 新增 NotificationController（list / unread-count / markRead / markAllRead / destroy）
- 整合通知觸發至 MemberBookingController、ProviderBookingController、CompleteFinishedBookings、ReviewController
- 新增 notifications / jobs / failed_jobs migration
- Docker Compose 加入 queue-worker、mailpit service
- DivingOffer 補上 provider() 關聯

前端
- 新增 notificationStore（Polling 30s/60s 自適應 + Page Visibility API）
- 新增 NotificationBell（未讀 Badge）、NotificationDrawer（側邊通知中心）
- main.js：auth store init 前置於 router.use()，修正 beforeEach guard 時序問題
- notificationAxios：依路徑動態選擇 member/coach token
- NotificationDrawer：改用 new URL().pathname 提取 action_url 路徑

OpenSpec
- 歸檔 notification-system change
- 同步 notification-core / notification-email / notification-triggers specs 至主規格
- 更新 booking-lifecycle / review-lifecycle spec（補充通知觸發 requirement）

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

app/Models/DivingOffer.php

@@ -3,6 +3,7 @@
 namespace App\Models;
 
 use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
 use Illuminate\Support\Facades\Storage;
 
 class DivingOffer extends Model
@@ -47,6 +48,11 @@ class DivingOffer extends Model
             : null;
     }
 
+    public function provider(): BelongsTo
+    {
+        return $this->belongsTo(User::class, 'provider_id');
+    }
+
     public function schedules()
     {
         return $this->hasMany(CourseSchedule::class, 'diving_offer_id');