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/Resources/StarterSplits/Core.split.json

@@ -4,7 +4,6 @@
   "createdAt" : "2020-01-01T00:00:00Z",
   "exercises" : [
     {
-      "category" : 0,
       "durationSeconds" : 0,
       "id" : "01DXF6DT00C4K0NY1NRCFPB3XY",
       "loadType" : 1,
@@ -12,11 +11,9 @@
       "order" : 0,
       "reps" : 10,
       "sets" : 4,
-      "weight" : 0,
-      "weightReminderWeeks" : 2
+      "weight" : 40
     },
     {
-      "category" : 0,
       "durationSeconds" : 0,
       "id" : "01DXF6DT001AY3SXTEYHA94MHZ",
       "loadType" : 1,
@@ -24,14 +21,13 @@
       "order" : 1,
       "reps" : 10,
       "sets" : 4,
-      "weight" : 0,
-      "weightReminderWeeks" : 2
+      "weight" : 40
     }
   ],
   "id" : "01DXF6DT001MA0TM7FHJZT098Z",
   "name" : "Core",
   "order" : 1,
-  "schemaVersion" : 1,
+  "schemaVersion" : 2,
   "systemImage" : "figure.core.training",
   "updatedAt" : "2020-01-01T00:00:00Z"
 }