fix(glass): split backdrop-on tier from Plex-art; make app-wide glass near-opaque

Root cause: html[data-backdrop="on"] and .glass-media shared ONE translucent tier, so a value tuned for
Plex art (meant to show its poster through) was forced onto the whole app — over the feed, the nav and
popovers read straight through it. Split them: the app-wide background-image tier is now near-opaque
(surface 88% / card 90% / menu 93% / blur 22px), while the Plex-art tier stays translucent (72/80/85/14).
Tuned live on the user's prod session (50% -> 72% was still too see-through; 88% reads clean). 0.60.2.

frontend/src/lib/releaseNotes.ts

@@ -14,6 +14,13 @@ export interface ReleaseEntry {
 }
 
 export const RELEASE_NOTES: ReleaseEntry[] = [
+  {
+    version: "0.60.2",
+    date: "2026-08-08",
+    fixes: [
+      "Follow-up: made the frosted panels solid enough over a background image that the feed no longer shows through the sidebar and menus.",
+    ],
+  },
   {
     version: "0.60.1",
     date: "2026-08-08",