add hot-reload yaml configuration changes

[Deepam02]

Fixes #282

Implements automatic configuration reloading when agent YAML files change on disk.

What's included:

• File watching with fsnotify and 500ms debounce for multiple rapid writes
• Validates new config before applying (falls back on error)
• Reloads instruction, description, and commands properties
• TUI notifications for reload events (started/success/failure)

What's NOT included:

• reloading Model or toolset changes

[Deepam02]

Are there any other agent fields which should be included in this PR?

Model and toolset reloading looks more complex, since it needs proper lifecycle handling and cleanup. Should that be done as a separate PR? I can take that up if it makes sense.

[jeanlaurent]

That's cool ! This allow agents self updating themselves