errors: classify CDP debugger-detach as transient (retry-able)

[gucasbrg]

Problem

classifyBrowserError does not list the Detached while handling command pattern (or the related No tab with id / Debugger is not attached to the tab), so when the daemon emits one of them under concurrent load, the CLI surfaces it to callers as a hard failure instead of going through the existing retry loop in sendCommandRaw.

The e2e test harness tests/e2e/browser-public.test.ts already treats these three patterns as transient and retries:

function isTransientBrowserDetach(result: CliResult): boolean {
  const text = `${result.stderr}\n${result.stdout}`;
  return /Detached while handling command|No tab with id|Debugger is not attached to the tab/i.test(text);
}

So the "transient" judgement is already established — it just was not reflected in the runtime classifier.

Real-world impact

A news collector pipeline that calls web read --url … for ~20 BBC RSS items in parallel (workers=3) hit ~30-50 % spurious 500 failures even though re-running the failed items individually succeeds instantly. With this patch, daemon-client retries them automatically and end-to-end success is ~100 %.

Change

• Add three patterns to EXTENSION_TRANSIENT_PATTERNS in src/browser/errors.ts.
• Add the same patterns to the existing positive case in src/browser/errors.test.ts. Vitest passes (7/7).

No behavioural change for callers that were already reaching the e2e helper; this just brings the runtime classifier into agreement with the e2e helper.