fix: revive pane watcher no-handoff watchdog

[brickfrog]

Revives the pane watcher per .choir/context/pane-watcher-revival-spec.md.

• Captures zellij pane ids from list-panes before/after diffs and persists them to .choir/pane-ids sidecars.
• Replaces the broken pane-viewport subscribe snapshot path with injected dump-screen --pane-id observation.
• Collapses no-handoff watchdog behavior to a single idle threshold and removes the in-pane prod path.
• Deletes the broken C/FFI subscribe subsystem and snapshot-file references.

Verify:

• moon test --target native
• ! grep -rn "spawn_zellij_pane_viewport_subscribe|pane_snapshot_path|choir-viewport-" src/
• ! grep -rn "worker_no_handoff_prod_text" src/
• ! grep -rn "subscribe.*pane-viewport" src/
• moon build src/bin/choir_lint --target native && _build/native/debug/build/src/bin/choir_lint/choir_lint.exe

Verification

Generated by Choir from commands executed in the leaf workspace.

• moon test --target native
  • exit: 0
  • head: 08b1244
  • output tail:

Total tests: 2009, passed: 2009, failed: 0.

• ! grep -rn "spawn_zellij_pane_viewport_subscribe\|pane_snapshot_path\|choir-viewport-" src/

  • exit: 0
  • head: 08b1244

• ! grep -rn "worker_no_handoff_prod_text" src/

  • exit: 0
  • head: 08b1244

• ! grep -rn "subscribe.*pane-viewport" src/

  • exit: 0
  • head: 08b1244