feat(system-service): add PM2 picker and platform selection

[KraoESPfan1n]

Summary

In this pull request, the following changes are made:

• Add explicit PM2 support to the system-service monitor, including Windows-compatible PM2 execution.

• Add configurable platform selection for system services (Linux / Windows Server) in monitor UI.

• Add PM2 process picker in monitor UI (socket-driven process list + refresh).

• Keep backward compatibility with existing system_service_name values.

• Add backend tests for PM2 state mapping and platform selection routing.

• Relates to Monitor pm2 #3011

• Related discussion: Monitor pm2 #3011 (comment)

Please follow this checklist to avoid unnecessary back and forth (click to expand)

• If there are Breaking change (a fix or feature that alters existing functionality in a way that could cause issues) I have called them out
• I have disclosed any use of LLMs/AI in this contribution and reviewed all generated content.
  I understand that I am responsible for and able to explain every line of code I submit.
• Any UI changes adhere to visual style of this project.
• I have self-reviewed and self-tested my code to ensure it works as expected.
• I have commented my code, especially in hard-to-understand areas (e.g., using JSDoc for methods).
• I added or updated automated tests where appropriate.
• Documentation updates are included (if applicable).
• Dependency updates are listed and explained.
• CI passes and is green.

Screenshots for Visual Changes

• UI Modifications: System Service monitor now supports explicit platform selection and PM2 process dropdown with refresh.
• Before & After: Not attached in this CLI submission.

Event	Before	After
UP	N/A	N/A
DOWN	N/A	N/A
Certificate-expiry	N/A	N/A
Testing	N/A	N/A

[github-actions]

Hello! This pull request does not follow the repository's PR template and is being closed automatically.