Phase 5 of CalendarView WinUI 3 parity upgrade

Parent tracking issue: (will be linked from epic)

Scope

Complete the selection model, formatting pipeline, and timezone handling.

Work items

• Selection: Align CalendarView_Partial_Selection.cs with WinUI, particularly the OnSelectedDatesChanging validation flow and TrackableDateCollection change tracking
• Format helpers: Align CreateDateTimeFormatter(), FormatWeekDayNames(), UpdateWeekDayNameAPName(), header text formatting with WinUI
• Timezone: Verify InitializeIndexCorrectionTableIfNeeded() handles all edge cases (Samoa timezone, DST transitions) correctly across platforms
• Header animation: Verify UpdateHeaderText(withAnimation) and ViewChanged/ViewChanging visual states
• Scroll animation: Implement ScrollToDateWithAnimation() (currently missing - only non-animated scroll exists)

Files to modify

• src/Uno.UI/UI/Xaml/Controls/CalendarView/CalendarView_Partial_Selection.cs
• src/Uno.UI/UI/Xaml/Controls/CalendarView/CalendarView_Partial.cs (format helpers)
• src/Uno.UI/UI/Xaml/Controls/CalendarView/CalendarView_Partial_TimeZone.cs
• src/Uno.UI/UI/Xaml/Controls/CalendarView/CalendarViewGeneratorMonthViewHost.cs (month label formatting)
• src/Uno.UI/UI/Xaml/Controls/CalendarView/CalendarViewGeneratorYearViewHost.cs (year label formatting)
• src/Uno.UI/UI/Xaml/Controls/CalendarView/CalendarViewGeneratorDecadeViewHost.cs (decade label formatting)

WinUI source reference

• dxaml/xcp/dxaml/lib/CalendarView_Partial_Selection.cpp
• dxaml/xcp/dxaml/lib/CalendarView_Partial.cpp (formatting section)
• dxaml/xcp/dxaml/lib/CalendarView_Partial_TimeZone.cpp
• Generator host .cpp files

Dependencies

Phase 4

Risk & Testing

• Risk: LOW-MEDIUM - formatting changes can cause locale-specific bugs but are isolated
• Size: Small-Medium PR (~200-300 lines)
• Testing: CalendarViewIntegrationTests locale-specific tests. Japanese/Arabic/Hebrew calendar tests. Samoa timezone scenario.