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

Shared/Model/Enums.swift

@@ -35,24 +35,6 @@ enum LoadType: Int, CaseIterable, Codable, Sendable {
     }
 }
 
-/// Which segment of a split an exercise belongs to — the split screen groups its
-/// exercise list by this. Persisted as its raw `Int` value; `main` is the default
-/// (and what older documents without the field decode to).
-enum ExerciseCategory: Int, CaseIterable, Codable, Sendable {
-    case main = 0
-    case warmup = 1
-
-    /// Order the categories appear on screen: warm-up first, then the main circuit.
-    static let displayOrder: [ExerciseCategory] = [.warmup, .main]
-
-    var displayName: String {
-        switch self {
-        case .main: "Main Circuit"
-        case .warmup: "Warm-up"
-        }
-    }
-}
-
 /// The kind of training a split represents — used to tag the Apple Health workout
 /// so it lands in the right category (and credits the rings correctly), and to pick
 /// a MET value when the phone has to estimate calories without watch sensor data.