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/visual-card.tsx

@@ -61,7 +61,6 @@ export function VisualOutputCard({ output }: { output: unknown }) {
 				dangerouslySetInnerHTML={{ __html: sanitizeSvg(result.svg) }}
 				data-testid="visual-svg"
 			/>
-			{result.notes && <p className="mt-2 text-sm text-muted-foreground">{result.notes}</p>}
 		</div>
 	);
 }