feat(chat): decouple primitives from LangGraph via runtime-neutral ChatAgent contract #408

Job	Run time
Library — lint / test / build	1m 25s
Cockpit — deploy smoke dry-run	1m 5s
Cockpit — secret-gated integration	1m 3s
Website — lint / build	1m 34s
Chat Agent — smoke	1m 17s
Cockpit — representative capability smoke	1m 17s
Website — e2e	2m 22s
Cockpit — build / test	1m 26s
Cockpit — build all examples	4m 47s
Cockpit — e2e	1m 55s
Deploy → Vercel	0s
Production smoke	0s
	18m 11s

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