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/admin/_shared.tsx

@@ -192,6 +192,11 @@ export function SettingsToggle({
         </div>
       </div>
       <Switch
+        // The visible label is a sibling `<p>` with no association to the
+        // Radix switch button, so a screen reader would announce a bare
+        // "switch, on/off". Name it explicitly — one fix covers every admin
+        // toggle that mounts this shared component.
+        aria-label={label}
         checked={checked}
         onCheckedChange={onCheckedChange}
         disabled={disabled}