Workout: auto-switch to today's program + Rest Day state

The Workout tab kept showing the last-used program (with its old
completion) regardless of the weekly schedule, so a rest day still
displayed a stale, fully-checked workout.

- On a new day, the active program now follows the weekly schedule
  (applyScheduledProgramForToday in resetSetsForNewDayIfNeeded).
- Add isRestDayToday + a Rest Day card shown when today has no scheduled
  program, with a "Work out anyway" override. Header reads "Rest Day".
- Daily set reset (KC-1) unchanged — no day starts pre-checked.

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

KisaniCal/Models/ExerciseModels.swift

@@ -313,10 +313,32 @@ class WorkoutViewModel: ObservableObject {
         let today = iso.string(from: Date())
         let last  = UserDefaults.kisani.string(forKey: kLastActiveDay)
         guard last != today else { return }
-        if last != nil { clearAllDoneSets() }   // skip the wipe on the very first launch
+        if last != nil {
+            clearAllDoneSets()              // skip the wipe on the very first launch
+            applyScheduledProgramForToday() // follow the weekly schedule on a new day
+        }
         UserDefaults.kisani.set(today, forKey: kLastActiveDay)
     }
 
+    /// The program assigned to today in the weekly schedule (nil = rest day).
+    var todaysScheduledProgram: WorkoutProgram? { program(for: Date()) }
+
+    /// True when a schedule exists but today has no program — a rest day.
+    var isRestDayToday: Bool {
+        let weekday = Calendar.current.component(.weekday, from: Date())
+        return !schedule.isEmpty && schedule[weekday] == nil
+    }
+
+    /// On a new day, make the active program match the day's schedule so the
+    /// Workout tab shows today's workout instead of yesterday's. Rest days leave
+    /// the active program untouched (the view shows a rest state instead).
+    private func applyScheduledProgramForToday() {
+        guard let scheduled = todaysScheduledProgram, scheduled.id != activeProgramId else { return }
+        activeProgramId = scheduled.id
+        activeSections  = scheduled.sections
+        save()
+    }
+
     /// Unchecks every set across all programs and clears the in-progress session.
     private func clearAllDoneSets() {
         for pi in programs.indices {