* fix(failover): classify HTTP 402 as rate_limit when payload indicates usage limit (#30484)
Some providers (notably Anthropic Claude Max plan) surface temporary
usage/rate-limit failures as HTTP 402 instead of 429. Before this change,
all 402s were unconditionally mapped to 'billing', which produced a
misleading 'run out of credits' warning for Max plan users who simply
hit their usage window.
This follows the same pattern introduced for HTTP 400 in #36783: check
the error message for an explicit rate-limit signal before falling back
to the default status-code classification.
- classifyFailoverReasonFromHttpStatus now returns 'rate_limit' for 402
when isRateLimitErrorMessage matches the payload text
- Added regression tests covering both the rate-limit and billing paths
on 402
* fix: narrow 402 rate-limit matcher to prevent billing misclassification
The original implementation used isRateLimitErrorMessage(), which matches
phrases like 'quota exceeded' that legitimately appear in billing errors.
This commit replaces it with a narrow, 402-specific matcher that requires
BOTH retry language (try again/retry/temporary/cooldown) AND limit
terminology (usage limit/rate limit/organization usage).
Prevents misclassification of errors like:
'HTTP 402: exceeded quota, please add credits' -> billing (not rate_limit)
Added regression test for the ambiguous case.
---------
Co-authored-by: Val Alexander <bunsthedev@gmail.com>