Straight ice: flat backdrop, crisp translucent panels, barely any gradients

The colourful multi-blob wash was too much and still didn't read as
frosted glass. Replaced with a cleaner material approach:

- Backdrop is now flat with a single faint top highlight (the only
  gradient left in it); the animated blobs and the four colour radials
  are gone.
- Panels are crisper and more translucent: cards 62%, panels 66%,
  sidebar 64% (now flat, no vertical gradient), study chrome 68%, tab
  bar 70% — with a bright 1px edge (--glass-edge), a light-from-above
  sheen (--glass-sheen) and the inset top highlight.
- Light mode is lighter: page #eef3fa pale ice, sidebar and cards
  frosted white; dark mode is a flatter, slightly lighter navy
  (#121a2c page, #1a2337 surfaces).
- Key-gate glows toned right down to match.

Contrast re-audited against the effective frosted backgrounds: 21/21 AA.
Suites: deck chrome 15/15, deck fixes 15/15, final ux 12/12, key gate
49/49, install sheet 64/64, retry 14/14, zoom 6/6, security 8/8, pwa
16/16.

README.md

@@ -112,10 +112,11 @@ no database, no data leaving your machine except the requests you send to Ollama
   list with per-folder counts, Settings/Dark mode pinned to the bottom). It **collapses** to a 68px
   icon rail (remembered in `localStorage`) and becomes a slide-in **drawer** behind a hamburger on
   phones; mobile also keeps the frosted header + iOS tab bar
-- **One navy palette pulled from the app icon, both themes**: light page `#f4f7fd` / sidebar
-  `#e9eff9` / border `#dce4f1`; dark page `#0e1424` / sidebar `#0a0f1c` / surfaces `#171f33` /
-  border `rgba(255,255,255,.12)`. Surfaces are frosted glass (translucent + `backdrop-blur`) over
-  the icon's navy backdrop.
+- **One palette pulled from the app icon, both themes**: light page `#eef3fa` (pale ice) /
+  sidebar and cards frosted white / border `#dce4f1`; dark page `#121a2c` / sidebar `#0c1322` /
+  surfaces `#1a2337` / border `rgba(255,255,255,.1)`. Surfaces are frosted glass — translucent with
+  `backdrop-blur`, a bright 1px edge and a light-from-above sheen — over a flat backdrop with a
+  single faint highlight.
   Text tiers are documented AA ratios (see below), and the cards fill the row with
   `repeat(auto-fill, minmax(280px, 1fr))` — no stranded cards, no dead space
 - Deck cards: title → muted metadata → neutral tags (difficulty carries the only colour:
@@ -727,10 +728,11 @@ Things I chose while building, with the reasoning:
     have no `folderId`), deleting a folder re-homes its decks instead of deleting them, and folder
     names travel in exports so an imported deck lands where it came from. 13 browser checks cover
     create → freeze → move → rename → delete → reload → import.
-18. **The visual language is glassmorphism, with restraint.** The icon's blue is the one accent
-    colour driving buttons and highlights; the backdrop is a navy wash; surfaces — sidebar, cards,
-    chrome, sheets — are frosted and translucent. Colour appears in activity tints and semantic
-    feedback only — pretty, but still readable and quiet.
+18. **The visual language is frosted ice, with restraint.** The icon's blue is the one accent
+    colour driving buttons and highlights; the backdrop is flat with a single faint top highlight,
+    and surfaces — sidebar, cards, chrome, sheets — are translucent glass with a bright edge and a
+    soft sheen. Colour appears in activity tints and semantic feedback only — pretty, but still
+    readable and quiet.
 19. **Custom CSS lives in `@layer components`, and glass uses Tailwind's backdrop utilities.**
     Two build-level traps, both found by looking at real screenshots: unlayered rules beat Tailwind
     utilities (which silently broke `fixed` on the feed), and a hand-written `backdrop-filter` gets
@@ -750,10 +752,11 @@ Things I chose while building, with the reasoning:
     pill CTAs, 18px radii and restrained shadows; the sidebar, cards and chrome are translucent
     glass over the backdrop. Deck cards got real hierarchy: title → muted metadata → tags → summary
     → secondary Study CTA, with secondary actions behind a quiet menu.
-23. **One fixed backdrop layer instead of per-page blobs.** The decorative wash used to be
+23. **One fixed backdrop layer, deliberately almost flat.** The decorative wash used to be
     rendered inside the content column, so on wide screens it was clipped into a visible hard edge.
-    It now lives in a single `position: fixed` layer (`.app-backdrop`, `z-index: -10`) in the
-    icon's navy and blue, and `body`'s colour matches its bottom so mobile overscroll shows no seam.
+    It now lives in a single `position: fixed` layer (`.app-backdrop`, `z-index: -10`): a flat ice
+    or navy base plus one faint highlight at the top — just enough for the glass to catch, without
+    turning into a gradient soup. `body`'s colour matches it so mobile overscroll shows no seam.
 24. **The UI was deliberately made quieter.** One accent colour (`accent-*`), a desaturated
     `frost-*` scale, hairline borders and flat surfaces replaced the saturated gradients and the
     seven-colour activity badges. Semantic colours (green/amber/red) survive only where they carry
@@ -789,9 +792,8 @@ Things I chose while building, with the reasoning:
     Desktop keeps the designed 12–14px field sizes.
 31. **The app icon drives the palette.** The navy rounded-square artwork in
     `assets/app-icon-source.jpeg` is the source of truth: `frost-*` is navy-tinted, the accent is
-    the snowflake blue, the backdrop is the same navy wash, the primary CTA is the icon blue (deep
-    in light mode, bright in dark), and every icon/splash/favicon is rendered from it by
-    `scripts/make-icons.mjs`. The sidebar, header, key gate, empty state and install sheet all show
+    the snowflake blue, the primary CTA is the icon blue (deep in light mode, bright in dark), and
+    every icon/splash/favicon is rendered from it by `scripts/make-icons.mjs`. The sidebar, header, key gate, empty state and install sheet all show
     the real artwork instead of the old monochrome snowflake tile.
 14. **`gpt-oss:120b` does all content work — but it cannot read images** (`this model does not
     support image input`), so `VISION_MODEL` has to stay a multimodal model (`gemma4:31b-cloud`).