[codex] Add Moonshot Kimi backend provider #6546

Job	Run time
build-and-check	3m 12s
test-integration-packages/internal	1m 8s
test-integration-packages/billing	1m 16s
test-integration-cli	48s
test-integration-packages/agent-runtime	45s
test-integration-sdk	1m 15s
test-integration-common	51s
test-integration-web	49s
test-packages/internal	47s
test-web	2m 21s
test-sdk	41s
test-cli	55s
test-common	52s
test-packages/billing	51s
test-packages/agent-runtime	52s
test-.agents	56s
	18m 19s

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