fix(a11y): switch names, contrast floors, and chart-toggle pressed state

- Admin SettingsToggle: name the Radix switch via aria-label so it no longer
  announces as a bare 'switch, on/off' (one shared component, six call sites).
- Replace the phantom text-destructive-foreground / text-warning-foreground
  utilities with the vetted destructive pattern (bg-destructive text-white
  dark:bg-destructive/60) and a readable foreground on the warning wash — no
  more dead classes riding on cascade order.
- Drop the sub-AA opacity tiers: lab sparkline + titration marker off
  muted/70, state icons (query-error, chart empty/error, med sort) off
  muted/60 to the full token so they clear the light-theme floor.
- Chart range toggles expose aria-pressed (lab, custom-metric, health, mood,
  compliance) so the active window is conveyed to assistive tech.

src/components/ui/query-error-card.tsx

@@ -40,7 +40,7 @@ export function QueryErrorCard({
         className="flex flex-col items-center justify-center gap-3 px-6 py-10 text-center"
       >
         <AlertTriangle
-          className="text-muted-foreground/60 h-8 w-8"
+          className="text-muted-foreground h-8 w-8"
           aria-hidden="true"
         />
         <p className="text-sm font-medium">{title ?? t("common.loadFailed")}</p>