feat: React Native (Expo) support

[khaledalam]

Summary

Adds React Native (Expo) support to avatoon without changing web behaviour. The same <Avatoon> component now renders on web (DOM <canvas> + HTMLAudioElement) and on React Native (@react-three/fiber/native via expo-gl + expo-av), selected automatically by a react-native package export condition — consumers import from 'avatoon' on both.

How it works

A platform split keeps the component tree platform-agnostic:

• src/platform/ — renderer seam. index.ts (web) re-exports Canvas/hooks/controls from @react-three/fiber + @react-three/drei; index.native.tsx re-exports from the /native entries. All components now import these from ../platform.
• src/audio/ — audio seam. An AudioClock interface with a web impl (HTMLAudioElement) and a native impl (expo-av: base64 WAV → temp file via expo-file-system, positionMillis interpolated into a smooth per-frame clock). AvatoonModel talks only to this interface.
• Build — vite.native.config.mjs emits a separate lib/native/index.es.js, resolving .native.* first and externalizing all native peers. package.json exports adds the react-native condition; expo peers are optional peer deps and react-dom is now optional.
• Type shims (src/types/native-modules.d.ts) let it typecheck without installing Expo.

Examples & docs

• examples/native/App.tsx — audio-synced lip-sync driven via ref.
• examples/native/GoalsExample.tsx — goal-based gestures (Normal / Muscle / Sleep).
• README gains a "📱 React Native (Expo)" section with a platform-difference table.

Tests / coverage

• Coverage 80% → 96% lines (92.9% statements); 51 tests (was 33).
• New expoAudioClock.spec.ts unit-tests the native audio clock via manual expo-av / expo-file-system mocks (wired through jest.config.js).
• Added web coverage for the imperative ref handle + play button, the camera fov frame loop, and the audio/viseme-driving path.

Verification

• ✅ lint, typecheck, tests, and web + native build all green.
• ⚠️ Verified it compiles, bundles, and resolves to the correct platform code (native bundle references @react-three/fiber/native + expo-av; web bundle unchanged). Not yet run on a real device/simulator — an Expo device test is recommended before release.
• Note: @react-three/drei/native's HDR Environment is more limited than web; R3F's native entry is most proven on the v8 line (React 18 / Expo 51), which the example pins.

Release note

Touches src/, so merging to main will publish. Suggest landing as a minor (1.10.0) — new feature, no breaking changes to the web API.

[khaledalam]

🎉 This PR is included in version 1.10.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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