Let routines rename exercises and repeat them for interval segments

An exercise's name is now a per-routine display name: a new optional
libraryName on ExerciseDocument (snapshotted onto WorkoutLogDocument at
plan time) keeps the link to the bundled library exercise, and every
figure/info/cue lookup resolves libraryName ?? name. Deliberately not
schema-bumped — an older app dropping the key only strands the
figure link, same rationale as activityType. Cache schema bumped to 9
for the new columns.

The picker no longer filters out exercises already in the routine
(an "×N" badge marks them instead), exercise rows gain a leading
Duplicate swipe that clones an entry in place, and the edit sheet gets
a Name field with the library exercise shown read-only above it.

Claude-Session: https://claude.ai/code/session_01H8VxUX4ckjU3vRF5M4L5FV

Workouts/Views/Exercises/ExerciseAddEditView.swift

@@ -23,6 +23,11 @@ struct ExerciseAddEditView: View {
 
     // Local editable state
     @State private var exerciseName: String
+    // The library exercise this row derives from — nil only when `exerciseName`
+    // doesn't (yet) match any bundled exercise. Set alongside `exerciseName` when
+    // the picker is used; carried through unchanged when the user just retypes the
+    // name in the TextField, so a rename keeps its figure/info link.
+    @State private var libraryName: String?
     @State private var loadType: LoadType
     @State private var minutes: Int
     @State private var seconds: Int
@@ -45,6 +50,8 @@ struct ExerciseAddEditView: View {
         // shows (and saves back) its whole part until UX #3's UI lands.
         let w = Int(exercise.weight)
         _exerciseName = State(initialValue: exercise.name)
+        _libraryName = State(initialValue: exercise.libraryName
+            ?? (ExerciseMotionLibrary.exerciseNames.contains(exercise.name) ? exercise.name : nil))
         _loadType = State(initialValue: exercise.loadTypeEnum)
         _minutes = State(initialValue: exercise.durationMinutes)
         _seconds = State(initialValue: exercise.durationSeconds)
@@ -59,7 +66,10 @@ struct ExerciseAddEditView: View {
     var body: some View {
         NavigationStack {
             Form {
-                Section(header: Text("Exercise")) {
+                Section(
+                    header: Text("Exercise"),
+                    footer: Text("You can rename this exercise for this routine — for example \"Warmup Walk\" for Treadmill. The animated figure and exercise guide still come from the original exercise.")
+                ) {
                     if exerciseName.isEmpty {
                         Button(action: {
                             showingExercisePicker = true
@@ -72,7 +82,10 @@ struct ExerciseAddEditView: View {
                             }
                         }
                     } else {
-                        ListItem(title: exerciseName)
+                        if let libraryName {
+                            ListItem(title: libraryName)
+                        }
+                        TextField("Name", text: $exerciseName)
                     }
                 }
 
@@ -172,7 +185,9 @@ struct ExerciseAddEditView: View {
             }
             .sheet(isPresented: $showingExercisePicker) {
                 ExercisePickerView { exerciseNames in
-                    exerciseName = exerciseNames.first ?? "Unnamed"
+                    let picked = exerciseNames.first ?? "Unnamed"
+                    exerciseName = picked
+                    libraryName = picked
                 }
             }
             .navigationTitle(exerciseName.isEmpty ? "New Exercise" : exerciseName)
@@ -197,9 +212,17 @@ struct ExerciseAddEditView: View {
         let newWeight = weightTens + weightOnes
         let durationSecs = minutes * 60 + seconds
 
+        // An emptied name falls back to the library exercise (or, failing that, the
+        // prior name) rather than saving a blank display name.
+        let trimmedName = exerciseName.trimmingCharacters(in: .whitespacesAndNewlines)
+        let finalName = trimmedName.isEmpty ? (libraryName ?? exercise.name) : trimmedName
+
         var doc = RoutineDocument(from: routine)
         if let idx = doc.exercises.firstIndex(where: { $0.id == exercise.id }) {
-            doc.exercises[idx].name = exerciseName
+            doc.exercises[idx].name = finalName
+            // nil when the name matches the library exercise (unrenamed) — keeps an
+            // unrenamed exercise byte-identical on disk.
+            doc.exercises[idx].libraryName = (libraryName == finalName) ? nil : libraryName
             doc.exercises[idx].sets = sets
             doc.exercises[idx].reps = reps
             doc.exercises[idx].weight = Double(newWeight)