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.

README.md

@@ -1398,6 +1398,27 @@ Things I chose while building, with the reasoning:
     phase-1 suite (43 checks, including the real route mapping against a stub Ollama returning a
     monthly-limit body, a two-device sync round-trip, and the generation guards below).
 
+63. **Frutiger Aero is the third theme.** Settings → Theme offers Light, Dark and Frutiger Aero.
+    Aero is not a dark/light variant — it replaces the palette (a sky gradient with a strip of
+    grass, glossy glass with the classic horizon gloss, aqua buttons) and the scene (the glacier
+    blobs become clouds, the orbs soap bubbles) — so the light/dark toggles (header, rail, chat
+    header) hide while it is on and the picker says so. The pre-paint script applies the class
+    before the first paint, the PWA status bar follows it (#3fa3e0), and its muted/frost text is
+    darker than Light's because those labels sit directly on the sky. Covered by the axe and
+    pixel-contrast scans in all three themes.
+
+62. **Accessibility: axe is clean everywhere, and contrast is measured on real pixels.** axe cannot
+    judge text on blurred glass — it reports those nodes as "incomplete" — so `tests/contrast.mjs`
+    samples the rendered pixels (dominant non-glyph colour per element) and compares it with the
+    computed text colour using the WCAG formula, skipping disabled controls (1.4.3 exempts them)
+    and content behind an open sheet. Fixes from that pass: the hidden file inputs are out of the
+    accessibility tree (aria-hidden + tabIndex -1; labelled buttons open them), the heading order is
+    right (deck/homework/smart-review cards are h2; LearningSection takes a level so it is h2 on the
+    library and h3 inside the dialog), the study and review feeds have landmarks, and the light
+    settings sheet — translucent over a dark scrim, where its muted text measured ~2.8:1 — got its
+    own more opaque surface (`--glass-sheet-bg`). Result: 0 axe violations and 0 below-minimum
+    findings across every screen, all three themes, phone and desktop.
+
 61. **Glass that sits still doesn't blur.** The MacBook got hot just browsing: the ice scene animates
     constantly, and every `backdrop-filter` surface re-runs its blur on every frame while the backdrop
     moves — the whole card and rail area was re-blurring the scene ~60 times a second. Measured on