feat(backend): update collections, config and migration tools

Update Payload CMS configuration, collections (Audit, Posts), and add migration scripts/reports.

apps/backend/data/webflow-export-sample.json

@@ -0,0 +1,50 @@
+{
+  "_comment": "Sample Webflow export data for testing migration script",
+  "_instructions": "Copy this file to webflow-export.json and fill in your actual data from Webflow",
+  "categories": [
+    {
+      "name": "Google小學堂",
+      "slug": "google-workshop",
+      "colorHex": "#4285f4"
+    },
+    {
+      "name": "Meta小學堂",
+      "slug": "meta-workshop",
+      "colorHex": "#0668e1"
+    },
+    {
+      "name": "行銷時事最前線",
+      "slug": "marketing-news",
+      "colorHex": "#34a853"
+    },
+    {
+      "name": "恩群數位最新公告",
+      "slug": "enchun-announcements",
+      "colorHex": "#ea4335"
+    }
+  ],
+  "posts": [
+    {
+      "title": "示例文章標題",
+      "slug": "sample-post",
+      "content": "<p>這是文章內容...</p>",
+      "publishedDate": "2024-01-15T10:00:00Z",
+      "postCategory": "google-workshop",
+      "featuredImage": "https://example.com/image.jpg",
+      "seoTitle": "SEO 標題",
+      "seoDescription": "SEO 描述",
+      "excerpt": "文章摘要..."
+    }
+  ],
+  "portfolio": [
+    {
+      "name": "示例網站名稱",
+      "slug": "sample-portfolio",
+      "websiteLink": "https://example.com",
+      "previewImage": "https://example.com/preview.jpg",
+      "description": "專案描述...",
+      "websiteType": "corporate",
+      "tags": "電商, SEO, 網站設計"
+    }
+  ]
+}