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/settings/integrations/withings-card.tsx

@@ -228,7 +228,7 @@ export function WithingsCard({
           <a
             href="/api/withings/connect"
             data-testid="withings-reconnect-banner"
-            className="border-warning/30 bg-warning/10 text-warning-foreground hover:bg-warning/20 block rounded-md border px-3 py-2 text-sm transition-colors"
+            className="border-warning/30 bg-warning/10 text-foreground hover:bg-warning/20 block rounded-md border px-3 py-2 text-sm transition-colors"
           >
             <span className="font-medium">
               {t("settings.integrations.withings.reconnect.banner.title")}

src/components/settings/sharing-section.tsx

@@ -204,7 +204,7 @@ function ShareLinksCard() {
                         {t("common.cancel")}
                       </AlertDialogCancel>
                       <AlertDialogAction
-                        className="bg-destructive text-destructive-foreground hover:bg-destructive/90"
+                        className="bg-destructive dark:bg-destructive/60 text-white hover:bg-destructive/90"
                         onClick={() => revokeMutation.mutate(link.id)}
                       >
                         {t("settings.sharing.revoke")}