feat: implement graceful shutdown for backend processes via stdin

[vcfgv]

📝 Pull Request Template

1. Related Issue

Closes # (issue number)

2. Type of Change (select one)

Bug Fix

3. Description

On Windows, ⁠taskkill was unable to achieve the same effect as ⁠Ctrl+C (KeyboardInterrupt) on macOS, leading to forced termination without proper cleanup.

Fix Details:

• Implemented IPC via ⁠stdin to control the process lifecycle.
• The server now accepts a termination signal through stdin, triggering the existing graceful exit logic.

4. Testing

• I have tested this locally.
• I have updated or added relevant tests.

5. Checklist

• I have read the Code of Conduct
• I have followed the Contributing Guidelines
• My changes follow the project's coding style

[hazeone]

LGTM