Touch devices blur the live backdrop instead of the baked layer

Mobile engines repaint background-attachment: fixed late (iOS treats it
as scroll), so the baked glass showed a stale crop of the wallpaper
until a tap forced a repaint - "some of the UI looks bugged until I
click it". On touch devices (max-width 639px or pointer: coarse) the
bake is dropped for a real backdrop-filter over the live scene, so the
bubbles blur through the glass as they pass and the position is correct
by construction. Hand-rolled frost fills keep their own tints there;
desktop keeps the baked layer (measured cheaper and verified correct).

Pinned with a touch-context check in the mobile suite (124 checks).
Contrast 0 findings, axe clean, chat 101/101, regression 44/44, i18n
13/13, native 33/33. Version 0.3.8, SW -> freezmo-v67.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "freezmo",
-  "version": "0.3.7",
+  "version": "0.3.8",
   "private": true,
   "license": "GPL-3.0-only",
   "scripts": {