v3: error cards across the app, friendly network errors, code quality pass

src/components/ErrorCard.tsx

@@ -0,0 +1,20 @@
+import type { ReactNode } from "react";
+
+export function ErrorCard({ title, message, actions }: {
+  title: string;
+  message: string;
+  actions?: ReactNode;
+}) {
+  return (
+    <div className="error-card-wrap">
+      <div className="error-card" role="alert">
+        <span className="error-card-icon">⚠</span>
+        <div className="error-card-body">
+          <h2 className="error-card-title">{title}</h2>
+          <p className="error-card-message">{message}</p>
+        </div>
+      </div>
+      {actions && <div className="error-card-actions">{actions}</div>}
+    </div>
+  );
+}