Fix Mini App pinch cadence

[ael-dev3]

Summary

• make Mini App pinch zoom depend on the total gesture instead of WebView event count
• retain the exact desktop-web response while smoothing large embedded-browser changes
• reset cumulative zoom state at every pointer and viewport lifecycle boundary
• add scene-level iOS/Android-style cadence, reversal, cancellation, and coincident-touch regression coverage

Verification

• 2,990 frontend tests passed serially
• 99 focused pointer/scene tests passed after final lifecycle coverage
• TypeScript typecheck passed
• production build passed
• npm audit reports zero vulnerabilities

No version bump; this remains Alpha 0.3.43.