[codex] Add Moonshot Kimi backend provider #619

Job	Run time
build-freebuff	1m 16s
build-and-smoke-freebuff-windows	2m 39s
e2e-slash-commands	1m 3s
e2e-ads-behavior	1m 1s
e2e-terminal-command	1m 4s
e2e-version	59s
e2e-startup	1m 16s
e2e-agent-startup	2m 23s
e2e-code-edit	52s
e2e-help-command	1m 14s
	13m 47s

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