feat(a11y): R9 focus foundation — glass shadow fix, focus-visible ring, highlight/selected split

S1 — recipe foundation:
- Move .glass/.glass-card/.glass-menu into @layer components so a JSX shadow-* utility overrides the
  glass box-shadow again; the ~9 dead shadow-* on glass surfaces (modals, menus, save-bar, chat) now
  paint their intended drop-shadow. Perf-mode and :hover overrides stay unlayered so they still win.
- Add a .selectable recipe: the hover tint menu/list rows already use, PLUS the app-wide
  focus-visible ring that was missing on non-input controls (the biggest a11y gap).
- Split the popover roving highlight from the selected state (AnchoredPopover): a selected/checked
  PopoverItem now gets a ring ONLY, so its resting paint (bg-accent fill / text-accent / checkbox)
  survives being highlighted instead of downgrading to a 35% tint or being recoloured. Fixes the 4
  review findings deferred from R10-S0 generically; drops the leftover per-consumer data-active ring
  in tableHeader.

S2 — worst offenders:
- Account-menu trigger + switch/add/sign-out rows adopt .selectable (visible keyboard focus).
- Saved-views rows: group-focus-within reveals the hover-only action buttons for keyboard users;
  aria-current on the active row; focus-visible ring on every button.
- The 3 invisible-focus inputs get an accent focus ring: SearchBar + ShareDialog via focus-within on
  the glass pill/row, AboutCell via focus-visible on the trigger.

Deferred to a later R9 sprint: the full unification of all ~14 selection idioms, a shared <NavItem>,
and .is-current/.chip recipes (no consumer yet in this pass).

Verified: tsc/eslint/prettier/knip/vitest (79) green; browser computed-style checks confirm the glass
shadow now wins, the focus outlines render (2px accent), and the split renders (selected ring-only,
unselected fill).

frontend/src/components/SearchBar.tsx

@@ -31,7 +31,7 @@ export default function SearchBar({
     if (onGo && !goDisabled) onGo();
   };
   return (
-    <div className="pointer-events-auto flex-1 min-w-0 max-w-xl h-11 pl-3 pr-2 rounded-2xl glass-menu flex items-center gap-2">
+    <div className="pointer-events-auto flex-1 min-w-0 max-w-xl h-11 pl-3 pr-2 rounded-2xl glass-menu flex items-center gap-2 focus-within:outline-2 focus-within:outline-accent/60">
       <Search className="w-4 h-4 shrink-0 text-muted" />
       <input
         value={value}