Timer: Add "Checklist on Timer" Feature to Android

I previously requested checklist visibility during timer sessions (marked done), but it's still unavailable on Android—unlike iOS version 13.11.0 (May 2025 update), where checklists appear directly on the timer screen. On Android, starting a timer for habits like my Night Routine hides the checklist, defeating the purpose for multi-step routines.

This is crucial for ADHD users: timers track total time, while on-screen checklists guide next steps without mental load or app-switching