dsh-remote 0.5.0: node settings, session-cookie edge auth, sign-in popup

- Settings → Remote devices → Node: type master|slave (stored in state, beats
  config role; Restart DSH button under systemd/launchd), origin (read-only:
  own origin / paired master), 'Master has an auth middleware' toggle
- middleware on: a non-DSH answer on the link (login redirect, 401/403, inline
  HTML) raises auth-required; the UI opens <master>/dsh-remote/signin in a popup,
  the user signs in to the proxy, one click hands the proxy session cookie back
  (postMessage, origin-checked, trusted origins only), link retries
- edge mode 'cookie': pasted authentik_proxy_… (or a whole Cookie header),
  rotated proxy cookies persisted back; pair.mjs/install-mac --edge cookie
- connectMaster serialised; a failed attempt never clears a finished link
- tests: cookie seed/mode, HTML login wall; e2e-signin against a fake proxy

lib/ws.mjs

@@ -201,6 +201,7 @@ export function connect(url, { headers = {}, timeoutMs = 15000, rejectUnauthoriz
         const err = new Error(`upgrade refused: HTTP ${res.statusCode}${loc} ${res.headers.location ? '' : body.trim().slice(0, 200)}`.trim())
         err.status = res.statusCode
         err.location = res.headers.location
+        err.contentType = String(res.headers['content-type'] || '')
         err.body = body
         reject(err)
       })