Show ready state after completing preparation before leave time

[jjoonleo]

Completed Preparation Ready State Plan

Goal

Make the alarm UI clearly show a ready/on-time state when all preparation steps are complete but the user still has time before the leave threshold.

Context

• SRD: preparation completion and lateness are separate concerns.
• SRD: while continuing before the leave threshold, UI should communicate "ready / time remaining to leave" rather than "late".
• Current AlarmScreen uses the last preparation step name as timerLabel when all steps are done and the user continues before the leave threshold.
• The top text does show time until leaving, but the center label can still look like the last preparation step is active.

Decisions

• Keep the completion dialog behavior: all steps done does not auto-finish.
• Keep late-continue mode once the leave threshold is crossed.
• Add an explicit ready/on-time label for the all-done, continuing, not-late state.

Steps

1. Add localized copy for the ready state, for example "Ready to go" in English and the agreed Korean equivalent.
2. In AlarmScreen._buildAlarmScreen, set timerLabel to the ready label when:
   • preparation.isAllStepsDone
   • _isContinuingAfterCompletion
   • isLate == false
3. Keep displayRemainingSeconds based on timeRemainingBeforeLeaving in that state.
4. Add/update widget tests for:
   • All done + continue + before leave threshold shows ready label and leave countdown.
   • All done + continue + after leave threshold shows late-continue label and overdue countdown.

Validation

• Run flutter test test/presentation/alarm/screens/preparation_flow_widget_test.dart.
• Verify both English and Korean generated localization files are updated after ARB changes.

Open Questions

• Confirm final Korean ready-state wording.