fix(ui): stronger frosted glass + frosted settings backdrop; declutter header

- Increase .glass blur (32px) so overlay menus (account) read as proper frosted glass.
- Blur the settings modal backdrop (overlay backdrop-blur) so the panel reliably
  frosts the content behind it instead of showing a sharp video through.
- Remove the now-redundant header buttons (dark/light, color scheme, grid/list) —
  they live in Settings → Appearance. Header keeps search, sync, bell, account.

frontend/src/components/SettingsPanel.tsx

@@ -54,7 +54,7 @@ export default function SettingsPanel({
   return (
     <div className="fixed inset-0 z-40 flex justify-end">
       <div
-        className={`absolute inset-0 bg-black/40 ${
+        className={`absolute inset-0 bg-black/30 backdrop-blur-lg ${
           closing ? "animate-[overlayOut_0.19s_ease_forwards]" : "animate-[overlayIn_0.2s_ease]"
         }`}
         onClick={close}