fix(feed): re-measure the bare row's first-paint estimate

Making it a single line halved its height (82 -> 46), which left the
virtualizer sizing a 60-item page ~2160px too tall.

frontend/src/components/VirtualFeed.tsx

@@ -12,11 +12,15 @@ const LIST_GAP = 4;
 // Estimated row heights before measurement; real heights are measured per-row so these only affect
 // the very first paint and the scrollbar's initial guess. Taken from measuring each mode in the
 // browser rather than guessed — a bad estimate makes the scrollbar jump as you scroll in.
+// RE-MEASURE these when a mode's layout changes: they have gone stale twice already, most recently
+// when the bare row became a single line and halved (82 -> 46). The card figures are the roughest
+// of the set by nature — a card's height follows its column width (measured ~307 at 3 columns,
+// ~301 at 4, taller still at 2), so no single constant is right for every window.
 const ROW_EST: Record<FeedView, number> = {
   cards: 340,
   cardsSmall: 257,
   rows: 115,
-  rowsCompact: 82,
+  rowsCompact: 46,
   tiles: 132,
 };