feat(chat): scroll polish + pin/bubble system #688

Job	Run time
Website — lint / build	1m 33s
Library — lint / test / build	1m 45s
Cockpit — e2e	2m 5s
Cockpit — build all examples	5m 29s
Website — e2e	2m 17s
examples/chat — python smoke	1m 21s
Cockpit — build / test	1m 47s
Cockpit — deploy smoke dry-run	1m 24s
Cockpit — representative capability smoke	1m 33s
Cockpit — secret-gated integration	1m 31s
Deploy → Vercel	0s
Production smoke	-1s
	20m 44s

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