Function classify 

pub fn classify(lock_path: &Path) -> AgentStatus

Classify the agent’s running state by inspecting <home>/running.lock.

• No lock → Stopped
• Lock present, parses, pid alive → Running
• Lock present but pid not alive (crash / SIGKILL / OOM) → Stale
• Lock present but unparseable / unreadable → Stale with pid: None (treat as stale rather than running so dashboards don’t paint dead agents green)