Make the frosted glass actually visible

The wash was far too faint for backdrop-blur to register, so the glass
read as flat navy. Now:

- The backdrop is a real colour field: four saturated blue/periwinkle/
  cyan radial blobs over the navy base, plus two slow animated blobs at
  higher opacity and less pre-blur, placed behind the content column.
- Surfaces are properly translucent instead of near-opaque: cards 62%,
  glass panels 68%, sidebar 68%, list groups 70%, study chrome 72%,
  tab bar 74%, mobile header 62%.
- Glass gets a specular top edge (inset 0 1px 0 --glass-top) so the
  surface catches light like real glass.
- Light --text-subtle darkened to #55647f so text still clears AA on the
  tinted glass (4.84:1 on the most saturated sidebar area).

Audit updated to the tinted backgrounds: contrast 21/21. 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.

app/globals.css

@@ -93,9 +93,10 @@
   --sidebar-divider: #d7e0ef;
   --hairline-soft: rgb(14 21 40 / 0.07);
   --glass-tint: rgb(255 255 255 / 0.55);
+  --glass-top: rgb(255 255 255 / 0.55);
   --text: #0e1526;          /* 16.9:1 on #f4f7fd */
   --text-muted: #4d5c78;    /* 6.3:1  */
-  --text-subtle: #5a6a86;   /* 5.1:1  */
+  --text-subtle: #55647f;   /* 5.6:1  */
   --hover: rgb(14 21 40 / 0.05);
   --sidebar-top: #eef3fb;
   --sidebar-bottom: #e5edf9;
@@ -135,6 +136,7 @@
   --sidebar-divider: rgb(255 255 255 / 0.1);
   --hairline-soft: rgb(255 255 255 / 0.08);
   --glass-tint: rgb(255 255 255 / 0.06);
+  --glass-top: rgb(255 255 255 / 0.08);
   --text: #e9eefb;          /* 15.4:1 on #0e1424 */
   --text-muted: #b7c3dc;    /* 10.4:1 */
   --text-subtle: #94a4c2;   /* 7.3:1  */
@@ -163,22 +165,23 @@
   --shadow-card-hover: 0 10px 28px -16px rgb(0 0 0 / 0.55), 0 1px 2px rgb(0 0 0 / 0.3);
 }
 
-/* Backdrop: the icon's navy base and blue wash, seen through frosted glass. */
+/* Backdrop: the icon's navy base with saturated blue/periwinkle/cyan blobs —
+   this is the colour the frosted surfaces are blurring. */
 :root {
-  --bd-sky: rgb(110 175 245 / 0.2);
+  --bd-a: rgb(96 160 250 / 0.5);
-  --bd-lilac: rgb(145 145 240 / 0.14);
+  --bd-b: rgb(150 150 245 / 0.42);
-  --bd-mint: rgb(110 210 230 / 0.12);
+  --bd-c: rgb(90 205 235 / 0.38);
-  --bd-top: #f8fafe;
+  --bd-top: #f7faff;
-  --bd-mid: #f2f6fd;
+  --bd-mid: #eef4fd;
-  --bd-bottom: #ecf1fb;
+  --bd-bottom: #e8f0fb;
 }
 .dark {
-  --bd-sky: rgb(60 130 230 / 0.14);
+  --bd-a: rgb(48 120 235 / 0.42);
-  --bd-lilac: rgb(110 115 235 / 0.1);
+  --bd-b: rgb(105 110 240 / 0.34);
-  --bd-mint: rgb(70 180 215 / 0.08);
+  --bd-c: rgb(50 165 220 / 0.3);
-  --bd-top: #111a2e;
+  --bd-top: #101a30;
-  --bd-mid: #0e1424;
+  --bd-mid: #0c1220;
-  --bd-bottom: #0a101d;
+  --bd-bottom: #080d18;
 }
 
 html,
@@ -245,53 +248,54 @@ body {
   overflow: hidden;
   pointer-events: none;
   background:
-    radial-gradient(135vw 110vh at 4% -30%, var(--bd-sky) 0%, transparent 72%),
+    radial-gradient(52vw 52vh at 12% 4%, var(--bd-a) 0%, transparent 68%),
-    radial-gradient(125vw 105vh at 104% -18%, var(--bd-lilac) 0%, transparent 70%),
+    radial-gradient(46vw 46vh at 94% 12%, var(--bd-b) 0%, transparent 66%),
-    radial-gradient(135vw 105vh at 38% 128%, var(--bd-mint) 0%, transparent 72%),
+    radial-gradient(56vw 52vh at 78% 98%, var(--bd-c) 0%, transparent 68%),
+    radial-gradient(44vw 44vh at 26% 82%, var(--bd-a) 0%, transparent 70%),
     linear-gradient(180deg, var(--bd-top) 0%, var(--bd-mid) 50%, var(--bd-bottom) 100%);
 }
 
-/* Two slow, very soft blobs for a little life behind the glass. */
+/* Two slow, saturated blobs so the glass always has colour to bend. */
 .app-backdrop::before,
 .app-backdrop::after {
   content: "";
   position: absolute;
   border-radius: 50%;
-  filter: blur(110px);
+  filter: blur(80px);
-  opacity: 0.22;
+  opacity: 0.55;
 }
 .app-backdrop::before {
-  width: 52vw;
+  width: 44vw;
-  height: 52vw;
+  height: 44vw;
-  min-width: 24rem;
+  min-width: 20rem;
-  min-height: 24rem;
+  min-height: 20rem;
-  top: -26vh;
+  top: 4vh;
-  left: -18vw;
+  left: 6vw;
-  background: radial-gradient(circle, var(--bd-sky), transparent 66%);
+  background: radial-gradient(circle, var(--bd-a), transparent 64%);
   animation: float 16s ease-in-out infinite;
 }
 .app-backdrop::after {
-  width: 46vw;
+  width: 40vw;
-  height: 46vw;
+  height: 40vw;
-  min-width: 22rem;
+  min-width: 18rem;
-  min-height: 22rem;
+  min-height: 18rem;
-  bottom: -28vh;
+  bottom: -6vh;
-  right: -14vw;
+  right: 2vw;
-  background: radial-gradient(circle, var(--bd-mint), transparent 66%);
+  background: radial-gradient(circle, var(--bd-c), transparent 64%);
   animation: float 20s ease-in-out infinite reverse;
 }
 .dark .app-backdrop::before,
 .dark .app-backdrop::after {
-  opacity: 0.3;
+  opacity: 0.6;
 }
 
 @layer components {
 /* Glass primitives ------------------------------------------------------ */
 .glass-panel {
   @apply backdrop-blur-xl backdrop-saturate-150;
-  background: color-mix(in oklab, var(--surface) 82%, transparent);
+  background: color-mix(in oklab, var(--surface) 68%, transparent);
   border: 1px solid var(--hairline);
-  box-shadow: var(--shadow-card);
+  box-shadow: var(--shadow-card), inset 0 1px 0 var(--glass-top);
 }
 
 .glass-chip {
@@ -307,7 +311,7 @@ body {
   /* Tailwind emits both the prefixed and standard properties; hand-written
      backdrop-filter gets minified down to -webkit- only, which paints nothing. */
   @apply backdrop-blur-xl backdrop-saturate-150;
-  background: color-mix(in oklab, var(--surface) 70%, transparent);
+  background: color-mix(in oklab, var(--surface) 62%, transparent);
   border-bottom: 1px solid var(--hairline);
 }
 
@@ -315,7 +319,7 @@ body {
    surface as the cards, with a neutral border and shadow. */
 .study-chrome {
   @apply backdrop-blur-xl backdrop-saturate-150;
-  background: color-mix(in oklab, var(--surface) 88%, transparent);
+  background: color-mix(in oklab, var(--surface) 72%, transparent);
   border: 1px solid var(--hairline);
   box-shadow: var(--shadow-card);
 }
@@ -326,9 +330,9 @@ body {
 .card {
   border-radius: 1.125rem;               /* 18px */
   @apply backdrop-blur-xl backdrop-saturate-150;
-  background: color-mix(in oklab, var(--surface) 78%, transparent);
+  background: color-mix(in oklab, var(--surface) 62%, transparent);
   border: 1px solid var(--card-border);
-  box-shadow: var(--card-shadow);
+  box-shadow: var(--card-shadow), inset 0 1px 0 var(--glass-top);
 }
 
 /* Opt-in hover lift for interactive cards (deck cards). Pointer devices only,
@@ -354,7 +358,7 @@ body {
 .list-group {
   border-radius: 1rem;
   @apply backdrop-blur-lg backdrop-saturate-150;
-  background: color-mix(in oklab, var(--surface) 82%, transparent);
+  background: color-mix(in oklab, var(--surface) 70%, transparent);
   border: 1px solid var(--hairline);
   overflow: hidden;
 }
@@ -407,7 +411,7 @@ body {
 
 .tabbar {
   @apply backdrop-blur-xl;
-  background: color-mix(in oklab, var(--page) 88%, transparent);
+  background: color-mix(in oklab, var(--page) 74%, transparent);
   border-top: 1px solid var(--hairline);
 }
 
@@ -428,8 +432,8 @@ body {
   @apply backdrop-blur-xl backdrop-saturate-150;
   background: linear-gradient(
     180deg,
-    color-mix(in oklab, var(--sidebar-top) 84%, transparent),
+    color-mix(in oklab, var(--sidebar-top) 68%, transparent),
-    color-mix(in oklab, var(--sidebar-bottom) 84%, transparent)
+    color-mix(in oklab, var(--sidebar-bottom) 68%, transparent)
   );
   border-right: 1px solid var(--sidebar-divider);
   box-shadow: var(--sidebar-edge);