fix: steer delivery renders bare in the transcript — no bubble, no model glue

Three refinements from live testing:

- Steer messages no longer sit inside the user Message container (the
  bubble background + right alignment it gave artifact cards). chat.tsx
  renders SubagentSteerCard directly in the transcript column — full
  width, centered, same register as the teacher's artifacts.
- Research steers render a quiet "Research complete · N sources" badge
  (the dispatch-settled idiom), not the full brief: briefs are long, the
  wake turn weaves them into the lesson anyway, and the full text stays
  persisted in the artifact part — a "view full research" affordance
  can be added later without any protocol change. Failures keep the
  failure card (the brief explains what went wrong).
- The sub-agents' verification notes (visual/demo builder notes) are
  model-facing glue and no longer render on success; failure notes
  remain the error explanation.

SSR-verified against a synthetic record: badge + SVG bare in the
transcript (no is-user wrapper), notes/brief confined to the RSC
payload. 229/229, typecheck, lint, build green.

components/artifacts/demo-card.tsx

@@ -99,10 +99,10 @@ export function DemoOutputCard({ output }: { output: unknown }) {
 			</div>
 		);
 	}
-	return <DemoFrame title={result.title} html={result.html} notes={result.notes} />;
+	return <DemoFrame title={result.title} html={result.html} />;
 }
 
-function DemoFrame({ title, html, notes }: { title: string; html: string; notes?: string }) {
+function DemoFrame({ title, html }: { title: string; html: string }) {
 	const actions = useContext(ChatActionsContext);
 	const iframeRef = useRef<HTMLIFrameElement | null>(null);
 	const [state, setState] = useState<DemoBridgeState>(INITIAL_DEMO_BRIDGE_STATE);
@@ -145,7 +145,6 @@ function DemoFrame({ title, html, notes }: { title: string; html: string; notes?
 				style={{ height: state.height ?? 360 }}
 				data-testid="demo-iframe"
 			/>
-			{notes && <p className="mt-2 text-sm text-muted-foreground">{notes}</p>}
 		</div>
 	);
 }