Ice scene: the glossy orbs become rising bubbles, ~38% more transparent

- Orbs rise from below the bottom edge to above the top edge, each with
  its own 36-68s pass (slower on phones), a negative delay (scene already
  populated on load), own horizontal position, a gentle sway and a slight
  scale drift; opacity fades in/out at the edges so the loop never pops.
- Only transform + opacity animate, each orb on its own composited layer
  (will-change: transform); no filter/backdrop-filter, nothing animates
  size/offsets/shadow. The glacier blobs are untouched.
- Opacity lowered ~38% in both themes: 0.55->0.34 light, 0.8->0.5 dark,
  phone overrides 0.32->0.2 / 0.42->0.26.
- prefers-reduced-motion: rise removed, orbs return to the old static
  placements (a paused-from-start CSS animation is not applied in Chrome
  and would park them below the fold); tab hidden: a visibility listener
  parks the whole scene (.ice-paused), blob drift included.
- Measured with a CDP perf trace on a 4x throttled phone profile: p95
  33.4ms, 0 frames over 34ms, no long tasks - identical to the pre-change
  baseline; ~0.6% extra main-thread CPU. Desktop stays compositor-bound
  from the pre-existing blob drift, as before. tests/bubble-perf.mjs
  keeps it repeatable.
- New bubbles suite (34 checks) in the repo harness; the axe contrast
  matrix is now 16 runs (360/390/1280 x dark/light x EN/CS) and passes.
- SW cache -> freezmo-v31; README decision 46.

Full suite: 11/11 suites, 424 checks.

README.md

@@ -1072,8 +1072,29 @@ Things I chose while building, with the reasoning:
     (native), i18n, the freeze loading screen, Smart Review, and phases 1–3 (backup/sync/usage
     limits, the learning engine, homework check/follow-ups). Suites that need a stub Ollama or
     VAPID keys start their own `next start` instance on a spare port, verify the port is free and
-    kill the process group on exit; test scratch stays in `tests/.tmp/` (gitignored). 379 checks
-    across the ten suites.
+    kill the process group on exit; test scratch stays in `tests/.tmp/` (gitignored). Eleven suites,
+    424 checks.
+
+46. **The ice orbs are rising bubbles now, composited and cheaper to read through.** The glossy
+    orbs (the glacier blobs stay exactly as they were) rise from below the bottom edge to above the
+    top edge, each with its own 36–68 s pass (slower on phones), a negative delay so the scene is
+    already populated on load, its own horizontal position, a gentle sway and a slight scale drift;
+    opacity fades in/out near the edges so the loop never pops. Only `transform` and `opacity`
+    animate, each orb owns a composited layer (`will-change: transform`), there is no
+    filter/backdrop-filter on them, and nothing animates size, offsets or shadow. Opacity dropped
+    ~38% in both themes (0.55→0.34 light, 0.8→0.5 dark; phone overrides 0.32→0.2 / 0.42→0.26) so
+    the background reads through while the gloss stays soft. Under `prefers-reduced-motion` the
+    rise is removed and the orbs return to their old static placements — a paused-from-the-start
+    CSS animation is not applied at all in Chrome (`getAnimations()` is empty), which would have
+    parked them below the fold; while the tab is hidden a visibility listener parks the whole scene
+    (`.ice-paused`), which also freezes the blob drift. Measured with a CDP performance trace on a
+    4× throttled phone profile (390×844 @2x): p95 33.4 ms, zero frames over 34 ms and no long tasks
+    — identical to the pre-change baseline — for ~0.6% extra main-thread CPU; the desktop scene
+    stays compositor-bound from the pre-existing blob drift, exactly as before. Verified by the
+    bubbles suite (34 checks: scene stacking/layout contract, keyframes only transform+opacity,
+    rise/sway/scale/fade phases, per-breakpoint counts 5/3/2, phone pacing, reduced motion,
+    tab-hidden parking) plus the 16-run axe contrast matrix (360/390/1280 × dark/light × EN/CS).
+    `tests/bubble-perf.mjs` keeps the measurement repeatable.
 
 36. **The mobile declutter pass reshapes, it doesn't fork.** Phones (≤639px) get a 3-step deck
     flow and a 2-step homework flow that share the exact state and handlers with the desktop