fix(ui): a card's Play clears its hover row at a large text size; Downloads links and the player description

At text size 1.3 a 242px feed thumbnail put the 63px Play 13px into the
hover row (the Play grows with the root font, the picture's height does
not). A picture narrower than 14rem centres the Play and the resume pair
above the row; the picture box is a size container for it.

The Downloads title and channel links were 21px tall inline boxes; they
stand on a 24px line now (B1). The player's description says a failed
load, with a retry, instead of 'No description' (both the side panel
and the popover).

frontend/src/components/VideoCard.tsx

@@ -35,6 +35,7 @@ import {
   MEDIA_BADGE,
   MEDIA_BAR,
   MEDIA_HOVER_LAYER,
+  MEDIA_PICTURE_CONTAINER,
   MEDIA_IMG,
   MEDIA_PICTURE,
   mediaTitleClass,
@@ -239,7 +240,7 @@ function Thumb({
     // min-h-0: the caller's aspect box must hold its ratio before the image arrives — an aspect-ratio
     // box otherwise grows to its content, and an off-screen, not-yet-loaded thumbnail measured 338px
     // tall, which stretched a whole Home shelf to it (ui/mediaCardStyles `mediaPictureBox`).
-    <div className={clsx("relative min-h-0", className)}>
+    <div className={clsx("relative min-h-0", MEDIA_PICTURE_CONTAINER, className)}>
       {/* Named by the title: its only text is the duration badge, so a screen reader heard the first
         Tab stop of every card as "44:10" (E28 S3d4). */}
       <a