feat: add Android ongoing notification support

[V3RON]

Summary

• add support for rich Android ongoing notifications, including progress updates, actions, and remote updates
• expose a server-side rendering API so apps can prepare Android ongoing-notification payloads outside the app runtime
• expand the example app and documentation to cover setup, testing, and managing ongoing notifications end to end

User Impact

• Android apps can now present persistent, richer notification experiences for flows like delivery tracking, rides, workouts, or other live status updates
• teams can generate notification payloads on the server and send them through their push provider for background updates
• developers have clearer docs and example flows for integrating, testing, and operating Android ongoing notifications