iPadLayout was rendering TodayView without workoutVM, crashing with
a fatal EnvironmentObject error on any device where hSizeClass goes
.regular (iPad, iPhone Plus/Max in landscape). Rewrote to use proper
NavigationSplitView with List(selection:) driving the detail column.
Also caches calendarIcon as a static func + @State instead of
recomputing UIGraphicsImageRenderer on every body evaluation.