Fixes CODAGT-484.
- Removed "quota", "billing", "insufficient_quota", "payment required"
from `authStrongPatterns`
- Added `usageLimitPatterns` slice with those patterns
- Added `usageLimitMatch` signal and rule between overloaded and
authStrong in priority
- Added terminal/retry messages for `ChatErrorKindUsageLimit`
- Simplified auth message (removed billing reference)
- Frontend: conditional `!usageLimitStatus.provider` guard on the "View
Usage" Alert
- Added `TestClassify_UsageLimitBeatsAuth` with 5 cases including real
production OpenAI error
- Added `ProviderQuotaExceeded` story asserting no "View Usage" link and
correct `ChatStatusCallout` rendering
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Cian Johnston
6acfe6c835