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/specs/development-environment/spec.md

@@ -0,0 +1,73 @@
+# Development Environment
+
+This capability defines the development environment setup and service management for Tool_OCR.
+
+## ADDED Requirements
+
+### Requirement: Unified Service Startup
+
+The system SHALL provide a single startup script that can launch all services or individual components.
+
+#### Scenario: Start all services
+
+- **WHEN** developer runs `./start.sh`
+- **THEN** both backend and frontend services start
+- **AND** service URLs are displayed
+
+#### Scenario: Start only backend
+
+- **WHEN** developer runs `./start.sh backend`
+- **THEN** only the backend service starts on port 8000
+
+#### Scenario: Start only frontend
+
+- **WHEN** developer runs `./start.sh frontend`
+- **THEN** only the frontend service starts on port 5173
+
+### Requirement: Service Process Management
+
+The system SHALL provide commands to check status and stop running services.
+
+#### Scenario: Check service status
+
+- **WHEN** developer runs `./start.sh --status`
+- **THEN** the script displays which services are running with their PIDs
+
+#### Scenario: Stop all services
+
+- **WHEN** developer runs `./start.sh --stop`
+- **THEN** all running services are gracefully terminated
+
+### Requirement: Environment Setup Validation
+
+The setup script SHALL validate that all required dependencies are correctly installed.
+
+#### Scenario: Validate Python environment
+
+- **WHEN** setup script runs
+- **THEN** Python version is checked (3.10+)
+- **AND** virtual environment is created or verified
+- **AND** all pip packages are installed
+
+#### Scenario: Validate Node.js environment
+
+- **WHEN** setup script runs
+- **THEN** Node.js LTS version is installed via nvm
+- **AND** npm dependencies are installed
+
+#### Scenario: Validate GPU support (optional)
+
+- **WHEN** setup script runs on a system with NVIDIA GPU
+- **THEN** CUDA version is detected
+- **AND** appropriate PaddlePaddle GPU version is installed
+- **AND** GPU availability is verified
+
+### Requirement: Environment Configuration
+
+The system SHALL use `.env.example` files to document all required environment variables.
+
+#### Scenario: New developer setup
+
+- **WHEN** developer clones the repository
+- **THEN** `.env.example` files document all required variables
+- **AND** developer copies to `.env.local` and fills in values