perf(ShaderView): pause render loop while app is backgrounded

[blazejkustra]

What

The requestAnimationFrame render loop kept running after the app was backgrounded, churning frames against an offscreen (and often transiently invalid) surface — wasting battery/GPU and, since #22, silently swallowing per-frame errors.

This tracks AppState in ShaderView and gates the render-loop effect on it:

• On a background transition, appActive flips false → the effect's existing cleanup (the cancelled token) tears the loop down.
• On return to the foreground, the effect re-runs and starts a fresh loop.

We pause only on a true background state — iOS inactive (app-switcher peek, notification pulldown) keeps running to avoid flicker on brief foreground interruptions.

Why this approach

It reuses the loop's existing teardown machinery (the per-run cancelled synchronizable) instead of adding a separate cross-runtime pause/resume channel, so there's no new state to keep in sync.

Verification (argent, iOS — iPhone 17)

1. Banners screen animating.
2. Home button → app backgrounded → loop torn down.
3. Re-foreground → animation resumes smoothly (coin counter advanced, lightning/fireworks at new phases across consecutive frames) — no freeze, no blank canvas.

Files

• src/components/ShaderView/index.tsx