Add minimal granularity support to CalendarView for Month/Year Picker controls

[Copilot]

CalendarView lacked granularity control, preventing its use as a Month or Year picker. When navigating the hierarchy (Century → Decade → Year → Month → Day), it always required drilling down to day selection.

Changes

• New CalendarMinimalGranularity enum: Day, Month, Year
• New MinimalGranularity property on CalendarView: Defaults to Day for backward compatibility
• Modified OnYearItemSelected behavior: Raises DateSelected event when reaching minimal granularity instead of continuing navigation
  • Year granularity: Selects DateTime(year, 1, 1) when clicking year in Decade view
  • Month granularity: Selects DateTime(year, month, 1) when clicking month in Year view

Usage

// Month Picker
var calendarView = new CalendarView 
{ 
    Mode = CalendarViewMode.Year,
    MinimalGranularity = CalendarMinimalGranularity.Month
};
calendarView.DateSelected += (s, e) => 
{
    // e.Date contains DateTime(year, month, 1)
};

// Year Picker
var calendarView = new CalendarView 
{ 
    Mode = CalendarViewMode.Decade,
    MinimalGranularity = CalendarMinimalGranularity.Year
};
calendarView.DateSelected += (s, e) => 
{
    // e.Date contains DateTime(year, 1, 1)
};

Warning

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Original prompt

---

This section details on the original issue you should resolve

<issue_title>Improve Ursa CalendarView</issue_title>
<issue_description>CalendarView should have a property describing the minimal granularity, for example mark it as "month" or year, then it can be used to select a month or a year. This is to support future controls like "Month Picker" and "Year Picker"

to support this, the OnYearItemSelected method should property handle these cases. when it reaches minimal granularity, select the date with day=1 or month=1 and day=1

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Improve Ursa CalendarView #874

---

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[github-actions]

Package	Line Rate	Branch Rate	Complexity	Health
Ursa	41%	31%	9051	✔
Ursa.Themes.Semi	61%	68%	1021	✔
Summary	49% (10700 / 21989)	34% (2644 / 7745)	10072	✔

[github-actions]

Test Results

718 tests  +3   718 ✅ +3   19s ⏱️ +4s
  2 suites ±0     0 💤 ±0 
  2 files   ±0     0 ❌ ±0 

Results for commit 9d9de3d. ± Comparison against base commit 13362d6.