Add best-of-n thinker subagent #4425

Job	Run time
build-and-check	3m 4s
test-integration-backend	59s
test-integration-packages/agent-runtime	1m 8s
test-integration-packages/internal	1m 0s
test-integration-cli	56s
test-integration-.agents	1m 1s
test-integration-npm-app	1m 2s
test-integration-web	1m 4s
test-integration-packages/billing	1m 2s
test-cli	1m 7s
test-integration-common	56s
test-backend	1m 2s
test-.agents	1m 5s
test-packages/internal	1m 1s
test-packages/agent-runtime	1m 9s
test-common	1m 0s
test-npm-app	1m 0s
test-packages/billing	1m 2s
test-web	1m 1s
	21m 39s

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