Navy theme from the app icon, frosted glass, and the new mark in-app

The icon's artwork is now the source of truth for the palette:

- frost-* is a navy-tinted neutral scale and accent-* is the icon's
  snowflake blue; light page #f4f7fd / sidebar #e9eff9 / border
  #dce4f1, dark page #0e1424 / sidebar #0a0f1c / surfaces #171f33.
- Surfaces are frosted glass: .card, .glass-panel, .list-group and
  .sidebar-surface are translucent with backdrop-blur/saturate, and the
  page wrapper no longer paints an opaque --page, so the fixed navy/blue
  backdrop reads through the sidebar, cards, chrome and sheets.
- The primary CTA is the icon's blue (#1d61ab in light, #59a8f7 in dark
  with ink text).
- The gate stage, fields and glows are navy/blue; viewport theme-color
  and the manifest background/theme colour are #0e1424.
- The old monochrome snowflake tile is gone from the brand: sidebar,
  header, key gate and empty state now show the real app icon (the
  install sheet already did). Decorative snowflakes stay.
- --surface-strong is finally defined (it was referenced but never
  declared, so those inputs had no fill).
- Icon URLs carry ?v=2 so browser favicon caches refetch.

Updated the contrast audit (21 pairs) and the deck-chrome token
assertions to the new theme. Verified: contrast 21/21, deck chrome
15/15, key gate 49/49, install sheet 64/64, final ux 12/12, retry
14/14, zoom 6/6, security 8/8, pwa 16/16, deck fixes 15/15.

components/ui.tsx

@@ -2,7 +2,6 @@
 
 import { forwardRef } from "react";
 
-import { SnowflakeIcon } from "@/components/icons";
 import { cn } from "@/lib/utils";
 
 type ButtonVariant = "primary" | "secondary" | "ghost" | "danger" | "success";
@@ -135,12 +134,17 @@ export function EmptyState({
 }) {
   return (
     <div className="animate-rise flex flex-col items-center px-6 py-6 text-center sm:py-24">
-      <span
-        className="mb-4 grid size-12 place-items-center rounded-2xl border border-[var(--hairline)] bg-[var(--surface-strong)] text-[var(--text-subtle)]"
-        aria-hidden
-      >
-        {icon ?? <SnowflakeIcon className="size-6" />}
-      </span>
+      {icon ? (
+        <span
+          className="mb-4 grid size-12 place-items-center rounded-2xl border border-[var(--hairline)] bg-[var(--surface-strong)] text-[var(--text-subtle)]"
+          aria-hidden
+        >
+          {icon}
+        </span>
+      ) : (
+        /* eslint-disable-next-line @next/next/no-img-element -- static app icon, no optimisation needed */
+        <img src="/icons/icon-192.png" alt="" aria-hidden className="mb-4 size-12 rounded-2xl" />
+      )}
       <h2 className="text-[17px] font-semibold tracking-[-0.01em] text-[var(--text)]">{title}</h2>
       {children ? (
         <p className="mt-2 max-w-md text-sm leading-relaxed text-[var(--text-muted)]">{children}</p>