login: fail-open recaptcha verify on infrastructure errors

verifyRecaptcha failed closed on ANY error from the Google siteverify call, so
a transient coinos<->Google network blip (or a Google slowdown) turned every
non-admin login into a "failed captcha" 401 until connectivity recovered — a
self-inflicted login outage from an external dependency.

Distinguish a real verdict from an infrastructure failure: fail CLOSED only on
a genuine success:false from Google; on a thrown error (network, timeout, 5xx)
fail OPEN and log it. Reaching Google is not part of authentication — the
password and the per-IP login rate limits still gate the request, and captcha
is only bot-mitigation, so allowing a login through when the verifier is
unreachable is the safer failure mode. Also bound the call with a 6s timeout so
a slow verifier can't hang the login.

Co-Authored-By: Claude Opus 4.8 <[email protected]>
Claude-Session: https://claude.ai/code/session_01XiwgmQKwKnRxUmVDd4xSf7

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