security: update Next.js to 15.5.11 to fix vulnerabilities #5623

Job	Run time
build-and-check	2m 53s
test-integration-packages/billing	1m 11s
test-integration-sdk	49s
test-integration-web	40s
test-integration-packages/internal	1m 1s
test-integration-common	45s
test-integration-cli	36s
test-integration-packages/agent-runtime	40s
test-packages/billing	47s
test-cli	50s
test-.agents	35s
test-web	46s
test-sdk	41s
test-common	39s
test-packages/internal	46s
test-packages/agent-runtime	41s
	14m 20s

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