browse-search.mjs only connected to the on-screen broadcast Chrome over
CDP, so browser-based Google search worked only during a live broadcast;
plain text turns fell through to the DDG cascade. Add a headless fallback
(system Chrome via channel:'chrome', else Playwright's bundled chromium)
for `search` mode so general conversation can use Google at no API cost.
`youtube` still requires the visible broadcast Chrome.
Detect Google's /sorry bot-detection interstitial structurally by URL and
fail fast so the caller fail-opens to DDG/Brave/Wikipedia instead of
treating the challenge page as empty results.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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