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>

Dockerfile

@@ -15,8 +15,8 @@ COPY api/ ./api/
 # 拷贝编译后的前端产物
 COPY api/webui/ ./api/webui/
 
-# 创建数据和日志目录
-RUN mkdir -p api/data api/logs
+# 创建日志目录
+RUN mkdir -p api/logs
 
 EXPOSE 23994