Fix pi-screen dead session handling

[ralphschuler]

Summary

Fix pi-screen so dead GNU screen sockets are not treated as resumable pi sessions.

Changes

• Parse the parenthesized screen -ls status and classify Attached, Detached, and Dead explicitly.
• Filter pi-screen session listings to live sessions only (Attached / Detached).
• When the repo-scoped session is dead, start a fresh repo session instead of running screen -r against the dead socket.
• Update pi-screen help/docs to describe live-session behavior.
• Add regression coverage for dead repo sessions and dead session names containing status words.

Validation

• node --test tests/unit/pi-screen.test.mjs
• npm run check

Risks/Rollback

Low risk: the change only filters dead/unknown screen entries from pi-screen management paths. Roll back by reverting this commit if live sessions are unexpectedly hidden.

Related Issues

None.

Conversation Context

User reported that pi-screen tries to reopen a dead repo session and should not rely on stale/cached screen state; each invocation should list current screens and ignore vanished sessions.