Put back gpt-5.1 for lite mode #5176

Job	Run time
build-and-check	2m 25s
test-backend	40s
test-packages/billing	40s
test-packages/internal	35s
test-integration-.agents	1m 23s
test-packages/agent-runtime	58s
test-.agents	39s
test-npm-app	39s
test-integration-cli	39s
test-integration-backend	40s
test-integration-packages/agent-runtime	39s
test-cli	1m 17s
test-integration-packages/billing	35s
test-integration-npm-app	46s
test-web	48s
test-common	49s
test-integration-sdk	57s
test-integration-packages/internal	47s
test-integration-web	42s
test-integration-common	48s
test-sdk	52s
	18m 18s

Provide feedback