All config file writes now use the write-temp + fsync + os.replace
pattern (KTD-4) so a crash mid-write leaves the original file intact.
- Add src/agentkit/server/utils/atomic_write.py with write_text_atomic
- settings.py: _write_yaml_config and _write_env_var use atomic write
- skill_service.py: import_skill uses atomic write
- skill_service.py: update_skill_config uses atomic write + fcntl.flock
around the read-modify-write cycle to serialize concurrent updates
- Add 11 unit tests covering happy path, crash safety, concurrency, errors
chiguyong