Fix syncthing startup and status regressions

[acmore]

Summary

• clean up owned local syncthing daemons on bootstrap failure
• signal detached sync readiness early enough for
  == Validate ==
  ✔ config: /Users/jacky.he/work/okdev/.okdev/okdev.yaml
  ✔ session: okdev-jacky-he
  ✔ namespace: default to show initial sync status
• use session-safe local syncthing listen addresses and bound mesh health probe collection

Testing

• env GOCACHE=/tmp/go-build go test ./internal/cli
• .venv/bin/pre-commit run --all-files --hook-stage manual okdev-gofmt