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

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

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

@@ -0,0 +1,25 @@
+# Change: Unify Environment Setup and Startup Scripts
+
+## Why
+
+目前專案有多個獨立的腳本來設置環境和啟動服務，開發者需要執行多個命令才能完整啟動專案。這增加了入門門檻並可能導致配置不一致的問題。
+
+Currently the project has multiple independent scripts for environment setup and service startup, requiring developers to run multiple commands to fully start the project. This increases the onboarding barrier and may lead to configuration inconsistencies.
+
+## What Changes
+
+- **Audit and update package lists**: Review and clean up `requirements.txt` and `frontend/package.json`
+- **Consolidate environment files**: Merge `.env` configuration across root and frontend directories
+- **Update setup script**: Improve `setup_dev_env.sh` with better error handling and dependency validation
+- **Create unified startup script**: Combine `start_backend.sh` and `start_frontend.sh` into a single `start.sh` with options
+
+## Impact
+
+- Affected files:
+  - `requirements.txt` - Python dependencies audit
+  - `frontend/package.json` - Node.js dependencies audit
+  - `setup_dev_env.sh` - Updated environment setup
+  - `start_backend.sh` - Will be replaced by unified script
+  - `start_frontend.sh` - Will be replaced by unified script
+  - `start.sh` - New unified startup script
+  - `.env*` files - Environment configuration cleanup