Change website/docs to say free model is GLM 5.1! #6086

Job	Run time
build-and-check	3m 2s
test-integration-packages/billing	1m 6s
test-integration-packages/internal	1m 39s
test-integration-common	45s
test-integration-cli	44s
test-integration-packages/agent-runtime	44s
test-integration-web	44s
test-common	41s
test-integration-sdk	1m 18s
test-packages/internal	52s
test-packages/agent-runtime	44s
test-sdk	42s
test-packages/billing	50s
test-cli	52s
test-.agents	42s
test-web	53s
	16m 18s

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