feat: make filename-based status management optional

[choplin]

Summary

• Make the filename-based status management feature optional
• Add new configuration option comment.status_management (default: false)
• Show warning messages when status management operations are attempted while disabled

Changes

• Added comment.status_management configuration option
• Updated file storage backend to respect the status_management setting
• Added warning messages for resolve/reopen operations when status management is disabled
• Updated tests to verify both enabled and disabled behavior
• Updated documentation

Behavior

• When status_management = false (default):

  • Files are saved without status prefixes (e.g., 1234567890.md)
  • Resolve/reopen operations show a warning and return false
  • Thread status is not tracked

• When status_management = true (with file storage backend):

  • Files use status prefixes (e.g., action-required_1234567890.md)
  • Status automatically updates based on comment authors
  • Resolve/reopen operations work as expected

Test plan

• All existing tests pass
• New test added for status_management = false behavior
• Manual testing with both settings