fix(design): claim audit part 1b — whole-row switches, the field-family edge, state-layer hovers, icon links, reason-disabled controls, 24/44 targets (E28)

- F12 (owner: A): SwitchRow, the whole settings row toggles; a Config boolean toggles from its title
  and hint (a label pointed at the switch).
- F14 (owner: B): the form dropdown trigger wears the field frame (see-through, the >= 3:1 edge);
  labelled pills keep the faint edge and the accent-edge hover. DESIGN says so, with log rows.
- F6: ~15 bg-card / bg-border / opacity hovers onto the B3 state layer; a lint rule (HOVER_SWAP)
  refuses the swap, contract-tested.
- F10: bare 14px icon links onto IconLink / LinkButton; a local lint rule refuses a glyph-only <a>.
- F13: reason-disabled controls are aria-disabled (Users, Channels backfill, Discovery, Scheduler
  runs, Config tests); FocusSafeButton now swallows the click of a caller's aria-disabled; the
  Config tests say why while dirty (testDirty, HU/EN).
- F5/F11: every control measured live at 24 (mouse) and 44 (coarse) across every page; touch-target
  is a utility that wins over a caller's min-h-6; link variants carry it too; SegmentedToggle,
  Tabs, NavRail, menu rows, PriorityStepper, sliders, CheckRow, InnerInput, card links and the rest.
- F9: DismissibleChip's label reaches the chip's 24; the Combobox chips are DismissibleChips.
- F15: the "+N" / "More..." open state worded as it renders.

frontend/src/components/channelCells.tsx

@@ -66,10 +66,12 @@ export function ActionsCell({
   const enabled = isAdmin || optInActionable;
   return (
     <div className="inline-flex items-center gap-2">
-      <Tooltip hint={backfillHint}>
+      {/* Unavailable with a reason (queued by someone else, already full): aria-disabled keeps it
+          focusable, so the hint that says why is reachable by keyboard too. */}
+      <Tooltip hint={backfillHint} always={!enabled}>
         <IconButton
-          onClick={!enabled ? undefined : isAdmin ? onReset : onDeep}
-          disabled={!enabled}
+          onClick={isAdmin ? onReset : onDeep}
+          aria-disabled={!enabled}
           variant={requested ? "ghost-accent" : "ghost"}
           label={isAdmin ? t("channels.row.resetBackfill") : t("channels.row.backfillThis")}
           noTitle