style(web): move the row-count select into the card header

It was sitting in a strip below the heading with a "Show" label and a "newest
first" hint — three lines of chrome for one control. The select now lives at the
right end of the card's own header bar (`margin-left:auto` inside the flex h2),
compact and case-normal so it reads as a control and does not grow the bar.
Label and hint are gone; the header text names the card, the values speak for
themselves, and screen readers keep the `aria-label`.

docs/WEB-UI.md

@@ -295,9 +295,9 @@ Gitea at most one call per 10s window; the VM columns are re-read on every
 refresh.
 
 Rows are ordered **newest first** (a queued run, which has no start time yet,
-sorts above everything; ties break on Gitea's run id). The **Show** selector in
-the card's header picks how many to list — 10 / 25 / 50 / 100, default from
-`[web].executions_limit` (10). The choice rides on the card's own polling URL
+sorts above everything; ties break on Gitea's run id). The row-count dropdown at
+the right end of the card's header bar picks how many to list — 10 / 25 / 50 /
+100, default from `[web].executions_limit` (10). The choice rides on the card's own polling URL
 (`/executions?limit=N`), so it survives every 5s refresh with no client-side
 state; a value set in the config outside those four is offered as an extra
 option rather than dropped.