Add day navigation to the Today board toolbar

Back/forward chevrons step the board a day at a time around the
existing calendar button, and a Today button — shown only when the
board is off today — jumps back. Also add the missing changelog
entries for the Today board itself.

Claude-Session: https://claude.ai/code/session_012qw2itfzKyEJ1HpsFt8Ex4

Workouts/Views/Today/TodayView.swift

@@ -123,12 +123,28 @@ struct TodayView: View {
             }
             .navigationTitle(isViewingToday ? "\(greetingLine) Today" : selectedDate.formatDate())
             .toolbar {
-                ToolbarItem(placement: .topBarLeading) {
+                ToolbarItemGroup(placement: .topBarLeading) {
+                    Button {
+                        shiftDay(by: -1)
+                    } label: {
+                        Label("Previous Day", systemImage: "chevron.backward")
+                    }
                     Button {
                         showingDayPicker = true
                     } label: {
                         Label("Go to Day", systemImage: "calendar")
                     }
+                    Button {
+                        shiftDay(by: 1)
+                    } label: {
+                        Label("Next Day", systemImage: "chevron.forward")
+                    }
+                    // Quick way home — redundant on today itself, so hidden there.
+                    if !isViewingToday {
+                        Button("Today") {
+                            withAnimation { selectedDate = Date() }
+                        }
+                    }
                 }
                 ToolbarItem(placement: .topBarTrailing) {
                     Button {
@@ -243,6 +259,14 @@ struct TodayView: View {
             .background(.secondary.opacity(0.15), in: Capsule())
     }
 
+    /// Step the viewed day back or forward (day precision; the time component is
+    /// irrelevant to the board).
+    private func shiftDay(by days: Int) {
+        withAnimation {
+            selectedDate = Calendar.current.date(byAdding: .day, value: days, to: selectedDate) ?? selectedDate
+        }
+    }
+
     // MARK: - Resolution helpers
 
     /// The live routine this schedule points at, following the seed clone-on-edit