style(frontend): Prettier config + one-time repo-wide format pass

Prettier 3 (pinned), printWidth 100, double quotes — chosen to match the existing
hand-formatting and minimise reflow. This commit is ONLY the mechanical format pass
(`prettier --write`) plus the config/ignore/scripts, isolated so it never pollutes a
feature diff. Verified behaviour-neutral: typecheck, eslint (0 errors), and vitest
all green before and after. See .git-blame-ignore-revs — `git blame` skips this sha.

frontend/src/components/SavedViewsWidget.tsx

@@ -62,9 +62,7 @@ export default function SavedViewsWidget({
   const [draftName, setDraftName] = useState("");
   const [renameId, setRenameId] = useState<number | null>(null);
 
-  const sensors = useSensors(
-    useSensor(PointerSensor, { activationConstraint: { distance: 4 } }),
-  );
+  const sensors = useSensors(useSensor(PointerSensor, { activationConstraint: { distance: 4 } }));
 
   // Keep the default-view mirror (read on load) in sync with the server state.
   useEffect(() => {