fix(managers): address the E4 S3 code-review round 3 findings

- The tag menu's "trigger is gone" test now measures against the SCROLLER, not the
  window. The page scroller starts ~230px down (measured), so a row that slid under
  the fixed toolbar was still "on screen" by window coords and the menu floated over
  the chrome, anchored to something invisible.
- Scroll-repositioning keeps whichever side the menu is anchored to instead of
  resetting it to "below" every frame — that reset made the layout effect flip it
  back, costing two renders and two forced layouts per frame near the bottom edge.
- One placement rule (`coordsFrom`) now serves the initial open, the layout
  correction and every reposition, so those can no longer drift apart.
- Card page: reset on the filter/sort INPUTS only, and separately COMMIT the clamp
  when the page falls out of range. Keying the reset on the row count (round 2) was
  too blunt — a background refetch that merely added a channel threw the reader off
  page 7 for something they didn't do.
- Pager derives `pageCount()` once and `hasPagerContent` reuses it, instead of the
  same expression twice in one file.
- Re-indent the pagerNode JSX left dangling by round 2's ternary edit.

frontend/src/components/Pager.tsx

@@ -7,12 +7,16 @@ import { ChevronLeft, ChevronRight } from "lucide-react";
 // size and slices its own rows; this only renders the controls and reports changes. `sizeLabel` lets
 // the caller say "Rows per page" or "Cards per page". Returns null when there's nothing to page.
 
+/** How many pages `total` rows make at `size` (`size <= 0` = "All" = one page). */
+function pageCount(total: number, size: number): number {
+  return size <= 0 ? 1 : Math.max(1, Math.ceil(total / size));
+}
+
 /** Whether a pager would render anything — the ONE owner of that rule. Callers that wrap the pager
  * in their own chrome gate on this instead of re-deriving it: a drifted second copy is exactly what
  * left empty control bands behind on tables with nothing to page. */
 export function hasPagerContent(total: number, size: number): boolean {
-  const totalPages = size <= 0 ? 1 : Math.max(1, Math.ceil(total / size));
-  return totalPages > 1 || total > 0;
+  return pageCount(total, size) > 1 || total > 0;
 }
 export default function Pager({
   page,
@@ -35,8 +39,7 @@ export default function Pager({
   sizeLabel: string;
 }) {
   const { t } = useTranslation();
-  const allRows = size <= 0;
-  const totalPages = allRows ? 1 : Math.max(1, Math.ceil(total / size));
+  const totalPages = pageCount(total, size);
   const safePage = Math.min(page, totalPages - 1);
 
   // Local text for the editable "jump to page" box (committed on Enter/blur).