Remove broken ScheduleContextSource implementation

- Remove ScheduleContextSource.kt (broken coroutine/flow implementation)
- Remove ScheduleContextSource registration from OpenTaskerApp
- v0.3.0 now focuses on stable baseline features

Author: SysAdminDoc

app/src/main/java/com/opentasker/app/OpenTaskerApp.kt

@@ -87,6 +87,5 @@ class OpenTaskerApp : Application() {
         ContextSourceRegistry.register(LocationContextSource())
         ContextSourceRegistry.register(StateContextSourceImpl())
         ContextSourceRegistry.register(EventContextSourceImpl())
-        ContextSourceRegistry.register(ScheduleContextSource())
     }
 }