feat: add data backup/import, goal step ordering, and PostgreSQL migration

- Add GET /api/backup/export and POST /api/backup/import endpoints for full data backup
- Add drag-and-drop reorder for goal steps with PUT /api/goals/{id}/steps/reorder
- Auto-assign sort_order on step creation (preserves creation order)
- Fix duplicate milestone rendering in goal detail page
- Add category management button in goal dialog
- Migrate database default from SQLite to PostgreSQL
- Fix router guard redirect loop for logged-in users on setup/login pages
- Fix ALTER TABLE ADD COLUMN crash on callable defaults (uuid.uuid4)
- Add auth status rate limiter and token version caching
- Update CLAUDE.md to reflect current architecture

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -1,14 +1,30 @@
-services:
-  elysia-todo:
-    build: .
-    container_name: elysia-todo
-    restart: unless-stopped
-    ports:
-      - "23994:23994"
-    volumes:
-      # 挂载前端编译产物，本地修改后可立即生效
-      - ./api/webui:/app/api/webui:ro
-      # 挂载数据库文件，持久化数据
-      - ./api/data:/app/api/data
-      # 挂载日志目录，方便查看日志
-      - ./api/logs:/app/api/logs
+services:
+  db:
+    image: postgres:18-alpine
+    container_name: elysia-todo-db
+    restart: unless-stopped
+    environment:
+      POSTGRES_USER: ToDoList
+      POSTGRES_PASSWORD: 53N2PTSjMBPDy6zY
+      POSTGRES_DB: ToDoList
+    ports:
+      - "5432:5432"
+    volumes:
+      - pgdata:/var/lib/postgresql/data
+
+  elysia-todo:
+    build: .
+    container_name: elysia-todo
+    restart: unless-stopped
+    ports:
+      - "23994:23994"
+    environment:
+      DATABASE_URL: "postgresql://ToDoList:53N2PTSjMBPDy6zY@db:5432/ToDoList"
+    depends_on:
+      - db
+    volumes:
+      - ./api/webui:/app/api/webui:ro
+      - ./api/logs:/app/api/logs
+
+volumes:
+  pgdata: