fix: recover failed worktree close teardown

[neumie]

Stacked on #157 (refactorx/full-headless).

Summary

• recover vanished before_worktree_remove hook terminals without timing out live hooks or leaving projects permanently stuck in closing state
• fail closed when PTY or persistent-session teardown cannot be verified, preserving the checkout for retry
• reconcile partial worktree removal, stale dtach/profile state, and replacement paths without deleting foreign data

Changes

Worktree close lifecycle

• add a daemon watchdog that uses PTY generation/liveness rather than elapsed duration
• atomically claim pending closes across OSC, PTY exit, and watchdog recovery for exactly-once resolution
• clear closing state, fail the monitor, notify the user, and preserve the worktree when a hook terminal disappears
• handle benign partial-removal residue while refusing to prune registrations if the original path was replaced

Terminal and session teardown

• move potentially stuck PTY readers/children into bounded background reaping
• add timeout-aware teardown flushing before destructive worktree operations
• verify tmux, screen, psmux, and dtach session exits; retain retry handles when process state is indeterminate
• reconcile orphaned profile-scoped sessions and account for Linux zombie processes

Runtime support

• give headless/UI-owned mode a separate log file
• replace per-pane terminal polling with activity events
• add regression coverage for aliases, partial removal, OSC/exit races, session termination, profile sockets, and reaper uncertainty

Test plan

• cargo fmt --all -- --check
• cargo test -p okena-terminal -p okena-daemon-core -p okena-git -p okena-core -p okena-workspace
• cargo test --bin okena log_rotation_tests
• cargo clippy --workspace --all-targets -- -D warnings
• Rust Analyzer diagnostics on the incident-critical files — no diagnostics
• post-rebase diff-preservation audit against origin/refactorx/full-headless
• independent read-only review — no blocking or major findings
• GitHub Build workflow