feat(worktree): suggest reparenting when Claude cd's into a worktree

[nek0der]

Summary

When Claude cds into a worktree the source tab doesn't own, surface a
bottom-anchored banner asking whether to move the tab there. Accept
reparents the source tab so the running pty follows the cd — no respawn,
no --resume. Useful when you tell Claude "make a worktree and work
there" and end up with the agent operating from a different cwd than the
tab that owns it.

• CwdChanged hook subscription — claude-shim/limpid-hook writes
  per-pane {oldCwd, newCwd, updatedAt} records into a new cwd-events
  directory; CwdEventTracker watches with DispatchSource (same shape
  as the existing agent / session trackers).
• 3-state matcher — RegisteredMatch enum distinguishes
  noRegisteredWorktreeContains (fall through to a git worktree list
  shell-out for unregistered worktrees), alreadyInsideSourceWorktree
  (no-op, no shell-out), and reparentTo(Kind) (surface the banner).
  Conflating the first two with a single nil would have produced
  duplicate worktree rows when the agent navigates around inside its
  own worktree.
• Active-tab gating — banner only surfaces while the source tab is
  the active tab. If a cd lands while the user is on a different tab,
  the suggestion is parked under that tab's id; landing on it later
  surfaces it. Leaving the tab while a banner is visible re-parks.
• didClosePane wiring — TabActions.closeTab / closeActivePane
  now route into CwdEventTracker and SessionTrackers carries a
  cwdEvent slot. A lazy sweep on activeTabDidChange catches close
  paths that don't thread the tracker through.

Related issue

Skip.

Checklist

• Builds locally (make build)
• Tests pass (make test)
• Tests added or updated where applicable
• Verified the change manually on macOS 26 (Tahoe)
• Code comments are in English
• CHANGELOG.md updated (under [Unreleased]) if user-visible