Frutiger Aero theme, pixel-measured contrast fixes, sheet surfaces

Frutiger Aero (Settings -> Theme): a third theme, not a dark/light variant.
A sky gradient with a strip of grass, the glacier blobs become clouds, the
orbs soap bubbles, glass gets the classic horizon gloss and the buttons a
glossy aqua. The light/dark toggles (header, rail, chat header) hide while it
is on and the picker says why; the pre-paint script applies the class before
first paint and the PWA status bar follows (#3fa3e0). Its muted/frost text is
darker than Light's because those labels sit directly on the sky.

Contrast, measured on real pixels (tests/contrast.mjs, now covering aero):
- The light settings sheet was translucent over a dark scrim, so its muted
  text measured ~2.8:1. Sheets and dialogs now use --glass-sheet-bg (a more
  opaque surface), and Light's --text-muted is a touch darker.
- Result: 0 below-minimum findings and 0 axe violations across every screen,
  all three themes, phone and desktop.

Also: the suites now seed the cookie notice as already dismissed (they run as
a returning user); the regression suite opts out to test the notice itself —
the previous deploy failed its gate because the notice blocked a chat chip
click. The notice also hides during immersive sessions (overlay-open), so it
can never cover a study feed.

Version 0.1.8, SW -> freezmo-v54.

components/ThemeSection.tsx

@@ -0,0 +1,45 @@
+"use client";
+
+import { useTheme, type Theme } from "@/components/ThemeToggle";
+import { haptic } from "@/lib/haptics";
+import { useI18n } from "@/lib/i18n";
+
+const OPTIONS: Array<{ id: Theme; labelKey: string }> = [
+  { id: "light", labelKey: "common.lightMode" },
+  { id: "dark", labelKey: "common.darkMode" },
+  { id: "aero", labelKey: "theme.aero" },
+];
+
+/**
+ * The theme picker: light, dark, or Frutiger Aero. Aero is not a dark/light
+ * variant — it swaps the whole palette and scene — which is why the light/dark
+ * toggles (header, rail, chat header) disappear while it is on.
+ */
+export function ThemeSection() {
+  const { theme, setTheme } = useTheme();
+  const { t } = useI18n();
+
+  return (
+    <section className="mb-4 space-y-3 rounded-2xl border border-[var(--hairline)] bg-[var(--surface-sunken)] p-3">
+      <h3 className="text-sm font-semibold text-frost-950 dark:text-frost-50">{t("settings.theme")}</h3>
+      <div className="segmented" role="group" aria-label={t("settings.theme")}>
+        {OPTIONS.map((option) => (
+          <button
+            key={option.id}
+            type="button"
+            aria-pressed={theme === option.id}
+            onClick={() => {
+              haptic("toggle");
+              setTheme(option.id);
+            }}
+          >
+            <span className="seg-label">{t(option.labelKey)}</span>
+          </button>
+        ))}
+      </div>
+      {theme === "aero" ? (
+        <p className="text-[11px] leading-snug text-[var(--text-subtle)]">{t("theme.aeroNote")}</p>
+      ) : null}
+    </section>
+  );
+}