fix: improve state detection accuracy and notification UX

- Hook reads JSON from stdin (not env vars) matching Claude Code protocol
- end_turn = Idle (not NeedsInput); real questions come from hooks
- Permission prompt (stale tool_use) never becomes Idle
- Notifications auto-expire after 10s (--expire-time)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

notify.go

@@ -22,6 +22,7 @@ func (n *ExecNotifier) Notify(title, body string) error {
 	return exec.CommandContext(ctx, "notify-send",
 		"--urgency=critical",
 		"--app-name=vmux",
+		"--expire-time=10000",
 		title,
 		body,
 	).Run()