refactor(feed): derive the row's drop-out thresholds from its column widths

They were two hand-written sets of numbers describing the same boxes —
change a w-32 and the thresholds are silently wrong, the symptom being a
column appearing just before it fits. Now computed from one table (which
reproduces the old values exactly).

Width also stops reaching the four views that ignore it: it changes every
frame of a resize, so passing it everywhere pushed all of them through
VideoCard's memo for nothing.

frontend/src/components/VideoCard.tsx

@@ -322,15 +322,33 @@ function Thumb({
   );
 }
 
-// What the one-line row needs before each column earns its place, cumulative from the left:
-// actions (192) + a title worth reading (~120) + gaps + the row's padding, then each column plus
-// its gap. Driven by the ROW's measured width, never the viewport — see VirtualFeed's itemWidth.
-const ROW_FITS = {
-  channel: 490,
-  meta: 606,
-  views: 682,
-  published: 886,
-};
+// The one-line row's column widths, in ONE place — the Tailwind classes below are generated from
+// them, so the thresholds can't drift out of step with the boxes they describe (they did when both
+// were written by hand). Each is measured against the worst case in the library AND in both
+// languages; see the row's own comment for where each number comes from.
+const ROW_COL = {
+  actions: 192, // w-48   — six buttons at 28 + five 4px gaps = 188
+  title: 120, //          — not a column: the floor below which a title isn't worth showing
+  channel: 128, // w-32
+  meta: 104, //            — RowMetaCells' own grid: 4rem + 1rem + 1rem + two 4px gaps
+  views: 64, //   w-16
+  published: 192, // w-48
+} as const;
+const ROW_GAP = 12; // gap-3
+const ROW_PAD = 26; // px-3 both sides, plus a rounding allowance
+
+// What the row must measure before each column earns its place — cumulative from the left, so each
+// one only appears once everything ahead of it AND a readable title already fit.
+const ROW_FITS = (() => {
+  let w = ROW_PAD + ROW_COL.actions + ROW_GAP + ROW_COL.title;
+  const at = (px: number) => (w += ROW_GAP + px);
+  return {
+    channel: at(ROW_COL.channel),
+    meta: at(ROW_COL.meta),
+    views: at(ROW_COL.views),
+    published: at(ROW_COL.published),
+  };
+})();
 
 function VideoCard({
   video,

frontend/src/components/VirtualFeed.tsx

@@ -180,7 +180,11 @@ export default function VirtualFeed({
                   key={v.id}
                   video={v}
                   view={view}
-                  width={itemWidth}
+                  // Only the one-line row reads its own width (it stands columns down as it
+                  // narrows). Everything else takes a stable 0, so a resize — which changes
+                  // itemWidth every frame — doesn't blow past VideoCard's memo for views that
+                  // wouldn't do anything with it.
+                  width={FEED_VIEW_SPEC[view].thumb ? 0 : itemWidth}
                   onState={onState}
                   onToggleSave={onToggleSave}
                   onOpenChannel={onOpenChannel}