Add machine comfort settings and tighten the document schemas

Machine-based exercises now carry ordered name/value comfort settings
(seat height, back-rest position, ...) on both ExerciseDocument and, as a
plan-time snapshot, WorkoutLogDocument — the optional array doubles as the
machine flag. Editable from the exercise editor's new Machine section and
from the workout row's settings sheet, whose mid-workout edits write back
to the originating split (workout saved first, so seed clone-on-edit
repointing can't clobber the log edit).

Schema tightening rides the same rev: splits bump to v2 (weight-reminder
fields and the unused exercise category removed), workouts to v3 (the
derived `completed` flag removed; status is the single source). Starter
seeds regenerated at v2 with unchanged ULIDs; SwiftData cache schema
bumped to rebuild. SCHEMA.md documents the shapes.

Claude-Session: https://claude.ai/code/session_01LEoff8bXGBS83tK1c55Mf7

Workouts Watch App/Views/WorkoutLogListView.swift

@@ -65,7 +65,10 @@ struct WorkoutLogListView: View {
                 }
             }
 
-            if doc.splitID != nil {
+            // Gate on the *resolved* split, not the stale `splitID` string — a split
+            // deleted on the phone leaves the id dangling, and offering Add Exercise
+            // against it would only show a misleading "All exercises added" picker.
+            if split != nil {
                 Section {
                     Button {
                         showingExercisePicker = true
@@ -84,7 +87,7 @@ struct WorkoutLogListView: View {
                 ContentUnavailableView(
                     "No Exercises",
                     systemImage: "figure.strengthtraining.traditional",
-                    description: Text(doc.splitID == nil
+                    description: Text(split == nil
                         ? "No exercises in this workout."
                         : "Tap + to add exercises.")
                 )
@@ -135,7 +138,6 @@ struct WorkoutLogListView: View {
             loadType: exercise.loadType,
             durationSeconds: exercise.durationTotalSeconds,
             currentStateIndex: 0,
-            completed: false,
             status: WorkoutStatus.notStarted.rawValue,
             notes: nil,
             date: doc.start