Add settings page with theme controls and commitment tracker

[dylan-kramer]

Summary

• add an AppProfile Isar collection and controller to persist theme preferences and all-time commitment stats
• expose dynamic light/dark themes with customizable accent colors driven from the stored profile
• create a motivating settings page with theme toggles, color picker, and commitment tracker that includes deleted contracts
• increment commitment stats when contracts succeed or fail and surface a settings entry point from the home page

Testing

• not run (Flutter SDK unavailable in container)

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Codex Task