fix: suppress unsupported BuilderId profile lookup

[stevensuna]

Summary

• cache a short-lived negative result when BuilderId profile lookup returns the unsupported AWS Builder ID 403
• suppress repeated ListAvailableProfiles calls during the cooldown while preserving refresh-token fallback
• downgrade repeated skipped profile resolution logs to debug to avoid warn spam during generation

Why

BuilderId accounts can generate successfully without a profile ARN, but ListAvailableProfiles may return:

HTTP 403: {"message":"AWS Builder ID is not supported for this operation.","reason":null}

Without caching that unsupported result, every generation retries the same failing lookup and emits repeated warnings/overhead.

Tests

• go test ./proxy -run 'TestResolveProfileArn|TestSetPayloadProfileArn|TestInitKiroHttpClient' -count=1
• git diff --check

Notes

• Full go test ./... currently fails in unrelated translator tests: TestClaudeToolResultMixedTextAndImage and TestOpenAIToolResultImageCarriedWhenFollowedByUser.