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

src/utils/apiError.ts

@@ -0,0 +1,10 @@
+/**
+ * Convert a caught fetch error into a human-readable message.
+ * TypeError means the request never left the client (no network / CORS / etc.).
+ */
+export function friendlyFetchError(err: unknown): string {
+  if (err instanceof TypeError) {
+    return "Could not connect to the server. Check your connection and try again.";
+  }
+  return err instanceof Error ? err.message : "An unexpected error occurred.";
+}