feat: unify environment scripts with start.sh

- Add unified start.sh script with subcommands (all/backend/frontend)
- Add process management (--stop, --status)
- Remove separate start_backend.sh and start_frontend.sh
- Update setup_dev_env.sh with pre-flight checks and --cpu-only/--skip-db options
- Update .env.example to remove sensitive data and add DIFY translation config
- Add .pid/ to .gitignore for process management

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

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

openspec/changes/archive/2025-12-02-unify-environment-scripts/design.md

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+# Design: Unify Environment Scripts
+
+## Context
+
+Tool_OCR 是一個 OCR 處理系統，包含 FastAPI 後端和 React 前端。目前的環境設置和啟動流程分散在多個腳本中：
+
+- `setup_dev_env.sh` (341 lines) - 完整的開發環境設置
+- `start_backend.sh` (60 lines) - 後端服務啟動
+- `start_frontend.sh` (41 lines) - 前端服務啟動
+- `download_fonts.sh` - 字體下載 (可選)
+
+**Current Pain Points:**
+1. 需要開兩個終端分別啟動前後端
+2. 環境變數配置分散在多個 `.env` 文件中
+3. 缺少服務狀態檢查和優雅停止機制
+4. GPU 配置需要手動驗證
+
+## Goals / Non-Goals
+
+**Goals:**
+- 簡化開發環境設置流程
+- 統一前後端啟動為單一命令
+- 改善錯誤訊息和故障排除體驗
+- 確保跨平台兼容性 (Ubuntu, WSL2)
+
+**Non-Goals:**
+- 容器化 (Docker) - 保留為未來提案
+- 生產環境部署腳本
+- 自動化測試環境設置
+
+## Decisions
+
+### 1. Unified Startup Script Design
+
+**Decision:** 使用單一 `start.sh` 腳本，支援多種模式
+
+```bash
+# Usage examples:
+./start.sh              # Start both backend and frontend
+./start.sh backend      # Start only backend
+./start.sh frontend     # Start only frontend
+./start.sh --stop       # Stop all services
+./start.sh --status     # Show service status
+```
+
+**Rationale:** 保持簡單，使用 bash 內建功能管理子進程，不引入額外依賴如 PM2 或 supervisord。
+
+### 2. Process Management
+
+**Decision:** 使用 PID 文件追蹤進程，支援優雅停止
+
+- PID files stored in `.pid/` directory (gitignored)
+- SIGTERM for graceful shutdown
+- Fallback to SIGKILL after timeout
+
+### 3. Environment Variable Strategy
+
+**Decision:** 保持分離的 `.env` 文件，但改善文檔
+
+- Root `.env.local` - 共用配置 (database, API keys)
+- Frontend `.env.local` - 前端特定配置 (VITE_* variables)
+- `.env.example` files updated with all required variables
+
+**Rationale:** 前端 Vite 需要 `VITE_` 前綴的變數，混合會造成困擾。
+
+### 4. Package Dependencies
+
+**Current State:**
+- Python: 77 packages in requirements.txt
+- Node.js: 17 dependencies + 15 devDependencies
+
+**Key Dependencies to Audit:**
+- PaddlePaddle GPU vs CPU selection
+- Unused development tools
+- Duplicate functionality packages
+
+## Risks / Trade-offs
+
+| Risk | Mitigation |
+|------|------------|
+| Breaking existing workflows | Keep old scripts as aliases |
+| Complex process management | Start simple, add features incrementally |
+| WSL2 compatibility issues | Test on clean WSL2 Ubuntu 22.04 |
+
+## Migration Plan
+
+1. Create new `start.sh` alongside existing scripts
+2. Update documentation to recommend new script
+3. After validation, deprecate old scripts (keep for one release)
+4. Remove old scripts in future version
+
+## Open Questions
+
+1. Should we add systemd service files for production?
+2. Should we include database migration in startup?
+3. Should we add health check retries before opening browser?