Web:
- New lib/billing-client.ts: factory wrapper using shared getAccessToken.
- Add @bytelyst/billing-client to web deps.
Mobile:
- New lib/billing-client.ts: factory wrapper using MMKV token storage.
- New lib/platform-api.ts: typed platform-client wrapper for settings,
sessions, and profile management.
- Add @bytelyst/billing-client and @bytelyst/platform-client to deps.
