One Shot Timers

[JonathanKChang]

Summary

Add a “Delete After Finishing” option for timers that removes one‑shot timers from storage automatically when they are dismissed. Addresses #433

Changes

• Alarm isolate
  • After stopping a timer, if timer.shouldDeleteAfterFinishing is true:
    • Load the persisted timer list, remove the finished timer, and save the updated list.
    • Notify the UI isolate via updatePort (updateTimers message) to refresh the timer list.
• Localization
  • Added timerDeleteAfterFinishingSetting string to app_en.arb.
• Settings schema
  • Introduced a new SwitchSetting named “Delete After Finishing” (default false) in timerSettingsSchema.
• Timer model
  • Exposed shouldDeleteAfterFinishing getter that reads the new setting.
• Timer card UI
  • Shows a small trash-can icon next to timers that have the one‑shot flag enabled.

Notes

• Implementation details:
  • Deletion happens in the background isolate that controls timer lifecycles, ensuring the UI does not need to manage the removal directly.
  • The UI receives a simple "updateTimers" message; existing UI code already handles generic timer‑list refreshes.