- Fail-fast guard in execution.ts: when daemon is running but extension
  is not connected, immediately surface a setup guide instead of waiting
  for the 30s connect timeout

- Extension version handshake: extension sends `hello` with its version
  on WebSocket connect; daemon stores it and exposes via /status; CLI
  warns on mismatch in both execution path and `opencli doctor`

- `opencli doctor` now shows extension version inline and reports
  version mismatch as an actionable issue

- Non-blocking npm update checker: registers a process exit hook so the
  update notice appears after command output (same pattern as npm/gh/yarn);
  background fetch writes to ~/.opencli/update-check.json for next run

- postinstall: print Browser Bridge setup instructions after shell
  completion install for first-time global install users

Bug fixes caught in review:
- discover.ts: add AbortController timeout to checkDaemonStatus() fetch,
  move clearTimeout after res.json() to cover body streaming
- daemon.ts: clear extensionVersion and reject pending requests in
  ws.on('error') handler, not just ws.on('close')
- update-check.ts: skip update notice when process exits with non-zero
  code; read cache once at module load to avoid double disk I/O;
  guard isNewer() against NaN from pre-release version strings

… hook