Enable OpenCode Zen for minimax + kimi; add buffbench agents #6508

Job	Run time
build-and-check	3m 4s
test-integration-packages/billing	1m 13s
test-integration-packages/internal	59s
test-integration-common	45s
test-integration-packages/agent-runtime	51s
test-integration-sdk	1m 19s
test-integration-cli	50s
test-.agents	50s
test-packages/internal	59s
test-web	3m 16s
test-packages/agent-runtime	48s
test-common	39s
test-cli	1m 10s
test-sdk	56s
test-packages/billing	44s
test-integration-web	53s
	19m 16s

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