Expand README with architecture and setup details

src/ui/StatusPill.tsx

@@ -0,0 +1,11 @@
+export type StatusPillTone = 'ok' | 'warning' | 'error' | 'checking' | 'muted';
+
+export interface StatusPillProps {
+  tone?: StatusPillTone;
+  children: string;
+}
+
+export function StatusPill({ tone = 'muted', children }: StatusPillProps) {
+  return <span className={`ui-status-pill ui-status-pill--${tone}`}>{children}</span>;
+}
+