[codex] Add spare time minimum warning

[jjoonleo]

Summary

• Add the Figma-designed minimum warning bubble to the onboarding spare-time field.
• Keep the spare-time input from decreasing below 10 minutes.
• Add localized warning text and a Widgetbook use case for the spare-time field.
• Tighten the shared error bubble layout so fixed-width message bubbles do not overflow.

Validation

• dart analyze lib/presentation/shared/components/error_message_bubble.dart lib/presentation/onboarding/schedule_spare_time/components/shcedule_spare_time_field.dart widgetbook/lib/schedule_spare_time_field.dart
• dart run build_runner build --delete-conflicting-outputs in widgetbook/
• flutter analyze in widgetbook/

Note: root flutter analyze still reports existing unrelated warnings/infos outside these changes.

[github-actions]

Visit the preview URL for this PR (updated for commit 7f32715):

https://ontime-c63f1--pr374-codex-spare-time-min-db0qb7uq.web.app

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[github-actions]

Visit the preview URL for this PR (updated for commit 7f32715):

https://on-time-front-widgetbook--pr374-codex-spare-time-min-kjxykjwx.web.app

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