feat(widget): calendar filter config + fix group-view data leak

Bug fix: publishWidgetSnapshot() now guards against activeGroup != nil,
so group view events/colors never contaminate the widget cache.

Feature: widgets can now be configured via long-press → Edit Widget.
- WidgetCalendar struct + writeCalendars/readCalendars in WidgetData.swift
- calendarKey added to WidgetEvent (backward-compatible decoder)
- CalendarIntent.swift: CalendarAppEntity + CalendarEntityQuery + CalendarSelectionIntent
- CalendarrTimelineProvider migrated from TimelineProvider to AppIntentTimelineProvider
- All 13 StaticConfiguration widgets changed to AppIntentConfiguration
- publishWidgetSnapshot() builds + writes the calendar list for the intent

An empty selection (default) shows all calendars; selecting specific
calendars filters the widget events accordingly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Calendarr iOS.xcodeproj/project.pbxproj

@@ -511,7 +511,7 @@
 					"$(inherited)",
 					"@executable_path/Frameworks",
 				);
-				MARKETING_VERSION = 2.7;
+				MARKETING_VERSION = 2.8;
 				PRODUCT_BUNDLE_IDENTIFIER = com.scarriffleservices.calendarr.ios;
 				PRODUCT_NAME = "Calendarr iOS";
 				STRING_CATALOG_GENERATE_SYMBOLS = YES;
@@ -555,7 +555,7 @@
 					"$(inherited)",
 					"@executable_path/Frameworks",
 				);
-				MARKETING_VERSION = 2.7;
+				MARKETING_VERSION = 2.8;
 				PRODUCT_BUNDLE_IDENTIFIER = com.scarriffleservices.calendarr.ios;
 				PRODUCT_NAME = "Calendarr iOS";
 				STRING_CATALOG_GENERATE_SYMBOLS = YES;