feat:實作 Member Portal MVP 前端與後端整合

後端：
- 新增 DivingOffer Model / DivingOfferController（列表+詳情 API，支援搜尋/篩選/分頁）
- 修正 Google OAuth callback 改為 redirect 至前端（SocialAuthController）
- 新增 config/cors.php 允許前端 origin
- .gitignore 新增 frontend/ 排除規則

前端（frontend/）：
- Vue 3 + Vite + Tailwind CSS + Pinia + Vue Router
- 頁面：首頁、課程列表、課程詳情、登入、註冊、個人資料、OAuth callback
- 整合至 Docker（multi-stage build，nginx 靜態服務於 port 5173）

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

config/cors.php

@@ -0,0 +1,34 @@
+<?php
+
+return [
+
+    /*
+    |--------------------------------------------------------------------------
+    | Cross-Origin Resource Sharing (CORS) Configuration
+    |--------------------------------------------------------------------------
+    |
+    | Here you may configure your settings for cross-origin resource sharing
+    | or "CORS". This determines what cross-origin operations may execute
+    | in web browsers. You are free to adjust these settings as needed.
+    |
+    | To learn more: https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS
+    |
+    */
+
+    'paths' => ['api/*', 'sanctum/csrf-cookie'],
+
+    'allowed_methods' => ['GET', 'POST', 'PUT', 'DELETE', 'OPTIONS'],
+
+    'allowed_origins' => [env('FRONTEND_URL', 'http://localhost:5173')],
+
+    'allowed_origins_patterns' => [],
+
+    'allowed_headers' => ['Content-Type', 'Authorization', 'Accept', 'X-Requested-With'],
+
+    'exposed_headers' => [],
+
+    'max_age' => 0,
+
+    'supports_credentials' => false,
+
+];