Consolidate task metrics to single source of truth

- Add API column name constants to WidgetDataManager (overdueColumn,
  dueWithin7DaysColumn, due8To30DaysColumn, etc.)
- Update DataManagerObservable to use WidgetDataManager column constants
- Remove duplicate ResidenceTaskStats struct, use TaskMetrics everywhere
- Delete TaskStatsCalculator.swift (consolidated into WidgetDataManager)
- Rename confusing flags: isUpcoming → isDueWithin7Days, isLater → isDue8To30Days
- Add comprehensive unit tests for TaskMetrics and WidgetTask

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

iosApp/iosApp.xcodeproj/project.pbxproj

@@ -138,7 +138,6 @@
 				Design/DesignSystem.swift,
 				Design/OrganicDesign.swift,
 				Helpers/ThemeManager.swift,
-				Shared/TaskStatsCalculator.swift,
 			);
 			target = 1C07893C2EBC218B00392B46 /* CaseraExtension */;
 		};