fix(a11y): chips, grips, the panel tab and Back to top keep the focus somewhere real

- F5: a chip's × pressed from the keyboard hands the focus to the next chip (else the previous one,
  else what follows) before it unmounts — in DismissibleChip, so all five chip rows get it
  (`focusNeighbour` in lib/useFocusKeeper).
- F4: a drag grip names what it lifts (`common.order.dragNamed`: panel groups, personal views);
  the two generic "Drag to reorder" keys are gone.
- F6: the side panel's edge tab is out of the Tab order while the card covers it, names its panel,
  and a keyboard pin moves the focus into the card.
- F7: Back to top is no Tab stop while hidden, and a keyboard press leaves the focus on the page.

frontend/src/components/ui/Chip.tsx

@@ -3,6 +3,7 @@ import type { ButtonHTMLAttributes, ReactNode } from "react";
 import clsx from "clsx";
 import { X } from "lucide-react";
 import { FocusSafeButton } from "./FocusSafeButton";
+import { focusNeighbour } from "../../lib/useFocusKeeper";
 import { chipClass, type ChipSize, type ChipVariant } from "./chipStyles";
 
 // The chip family (docs/DESIGN.md "One primitive per button family"): a small rounded-full token that
@@ -113,7 +114,14 @@ export function DismissibleChip({
       )}
       <FocusSafeButton
         type="button"
-        onClick={onDismiss}
+        onClick={(e) => {
+          // From the keyboard the × holds the focus, and the chip unmounts: hand the focus to the
+          // next chip (else the previous one, else what follows the row) first, not to <body> (E28
+          // review F5). A mouse press on it leaves the focus where it was.
+          const chip = e.currentTarget.parentElement;
+          if (chip && e.currentTarget === document.activeElement) focusNeighbour(chip);
+          onDismiss();
+        }}
         aria-label={dismissLabel}
         title={dismissLabel}
         className="-my-px grid size-6 shrink-0 place-items-center rounded-full transition state-layer touch-target"