Add auto-pause when the user is away from the keyboard

[haaaashimi]

Summary

• Added idle-based auto-pause so the work timer stops when there is no keyboard or mouse input for the configured threshold.
• Added settings to enable/disable away detection and tune the idle threshold.
• Preserved manual pause separately from idle pause, and resume now continues from the paused work timer unless the away time reaches the break duration, in which case the next work interval resets.

Testing

• Not run (not requested)
• Verified the main and settings scripts for syntax issues during implementation