feat: implement task management module

Backend (FastAPI):
- Database migration for spaces, projects, task_statuses, tasks tables
- SQLAlchemy models with relationships
- Pydantic schemas for CRUD operations
- Spaces API: CRUD with soft delete
- Projects API: CRUD with auto-created default statuses
- Tasks API: CRUD, status change, assign, subtask support
- Permission middleware with Security Level filtering
- Subtask depth limit (max 2 levels)

Frontend (React + Vite):
- Layout component with navigation
- Spaces list page
- Projects list page
- Tasks list page with status management

Fixes:
- auth_client.py: use 'username' field for external API
- config.py: extend JWT expiry to 7 days
- auth/router.py: sync Redis session with JWT expiry

Tests: 36 passed (unit + integration)
E2E: All APIs verified with real authentication

OpenSpec: add-task-management archived

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/README.md

@@ -0,0 +1,92 @@
+# PROJECT CONTROL Backend
+
+FastAPI 後端服務
+
+## 系統需求
+
+### 必要服務
+
+| 服務 | 版本 | 說明 |
+|-----|------|-----|
+| Python | 3.11+ | 執行環境 |
+| MySQL | 8.0+ | 主要資料庫 |
+| Redis | 6.0+ | Session 存儲 |
+
+### Redis Server 安裝
+
+Redis Python 套件 (`redis==5.0.1`) 僅為客戶端，需另外安裝 Redis Server：
+
+**macOS (Homebrew):**
+```bash
+brew install redis
+brew services start redis
+```
+
+**Ubuntu/Debian:**
+```bash
+sudo apt update
+sudo apt install redis-server
+sudo systemctl start redis-server
+sudo systemctl enable redis-server
+```
+
+**Docker:**
+```bash
+docker run -d --name redis -p 6379:6379 redis:alpine
+```
+
+**驗證安裝:**
+```bash
+redis-cli ping
+# 應回傳 PONG
+```
+
+## 環境建置
+
+```bash
+# 使用 Conda
+conda env create -f environment.yml
+conda activate pjctrl
+
+# 或使用 pip
+pip install -r requirements.txt
+```
+
+## 設定
+
+複製並編輯環境變數：
+```bash
+cp .env.example .env
+```
+
+主要設定項目：
+- `MYSQL_*` - 資料庫連線
+- `REDIS_*` - Redis 連線
+- `JWT_SECRET_KEY` - JWT 簽名密鑰 (生產環境必須更換)
+- `AUTH_API_URL` - 外部認證 API
+
+## 執行
+
+```bash
+# 開發模式
+uvicorn app.main:app --reload --port 8000
+
+# 生產模式
+uvicorn app.main:app --host 0.0.0.0 --port 8000
+```
+
+## 資料庫遷移
+
+```bash
+# 升級至最新版本
+alembic upgrade head
+
+# 回滾一個版本
+alembic downgrade -1
+```
+
+## 測試
+
+```bash
+pytest -v
+```