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/lib/useCardPager.ts

@@ -25,8 +25,7 @@ export function useCardPager<T>(rows: T[], sizeKey: string, enabled: boolean) {
     if (enabled && page > totalPages - 1) setPage(totalPages - 1);
   }, [enabled, page, totalPages]);
 
-  const paged =
-    !enabled || size <= 0 ? rows : rows.slice(safePage * size, safePage * size + size);
+  const paged = !enabled || size <= 0 ? rows : rows.slice(safePage * size, safePage * size + size);
 
   return {
     paged,