feat(drawer): add View section to switch Month/Week/Day

The slide-out panel gains a "View" section mirroring the top-bar switcher
pill: three NavigationDrawerItems (Month/Week/Day) with the current view
highlighted; tapping one selects that view and closes the drawer. The pill
stays as-is for quick cycling.

Centralise each view's label + icon as labelRes/icon extensions on
CalendarView so the pill and the drawer share one mapping. The drawer's
"Today" jump is dropped — the top-bar Today action and error-state retry
still cover it.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/src/main/res/values-de/strings.xml

@@ -187,6 +187,7 @@
     <string name="view_month">Monat</string>
     <string name="view_week">Woche</string>
     <string name="view_day">Tag</string>
+    <string name="view_section">Ansicht</string>
 
     <!-- Kalender-Filter (M3) -->
     <string name="filter_title">Kalender</string>