fix(pty): allow ticket-authorized ownership takeover

[jlongster]

Summary

• Let a valid, unexpired handoff ticket replace a live owner immediately, consuming the ticket atomically.
• Track ownership generations so superseded connections cannot prepare handoffs, stop the daemon, or clear successor ownership on disconnect.
• Add regression coverage for terminal continuity, stale-owner cleanup and commands, ticket expiry, and concurrent claimants; document the updated handoff contract.

Validation

• Formatting, Clippy, and all 35 tests passed on the original base.
• Use CI for validation against the latest master; local rebuild stopped as requested.

Rollout

Requires an updated PTY daemon build. Already-running older daemons retain the previous handoff behavior.