docs(chat): clarify injectThreadRouting usage prerequisites #1821

Job	Run time
CI scope	1m 36s
Website — e2e	54s
examples/ag-ui — e2e	45s
Website — lint / build	58s
Cockpit — build / test	0s
examples/chat — e2e (${{ matrix.shard }}/4)	0s
Library — lint / test / build	0s
Cockpit — build all examples	0s
Cockpit — e2e dispatcher	0s
Cockpit — secret-gated integration	0s
PostHog — dashboards-as-code drift check	0s
Cockpit — representative capability smoke	0s
Cockpit — e2e (${{ matrix.cap.angular }})	0s
examples/chat — python smoke	0s
Cockpit — deploy smoke dry-run	0s
examples/chat — e2e	0s
Canonical demo → Vercel	0s
Cockpit — e2e	0s
ag-ui demo → Vercel	1s
CI — required	3s
Deploy → Vercel	1s
Production smoke	1s
	4m 19s

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