Fix anthropic to open router mapping for opus 4.6 #5756

Job	Run time
build-and-check	2m 49s
test-integration-packages/internal	1m 3s
test-integration-packages/billing	1m 7s
test-integration-sdk	39s
test-integration-web	45s
test-integration-common	40s
test-integration-packages/agent-runtime	39s
test-integration-cli	49s
test-.agents	46s
test-sdk	44s
test-packages/agent-runtime	42s
test-common	48s
test-web	43s
test-cli	48s
test-packages/billing	42s
test-packages/internal	42s
	14m 26s

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