Calendar: fix week/3-day dead space (pin content to top)

The timeline views' content is a thin header + a greedy ScrollView (≈0 ideal
height), so the top-level VStack shrank and the bottomTrailing ZStack floated
it to the bottom — leaving a big empty gap above the day header. Month view
has a tall fixed grid so it never surfaced. Pin the VStack to fill height and
top-align.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

KisaniCal/Views/CalendarView.swift

@@ -392,6 +392,9 @@ struct CalendarView: View {
                     calDayTaskListView
                 }
             }
+            // Pin to the top so views whose content doesn't fill the height
+            // (week / 3-day timelines) don't float to the bottom of the ZStack.
+            .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .top)
 
             FAB { showAddTask = true }
                 .padding(.trailing, 20).padding(.bottom, 10)