Record per-set actuals and drive the chart and volume from them

Every completed set now writes a SetEntry (reps/weight or seconds),
pre-filled from the plan by transition(to:) so the list checkbox, both
run flows, and One More all capture for free; reset clears, skip keeps
partials. The rest and finish pages show the just-done set as a pill
that opens a stepper sheet for correcting reps and weight (2.5 lb /
1.25 kg steps). The Weight Progression chart plots the top-set actual
weight and workout volume sums recorded sets, both falling back to the
plan for legacy logs via effectiveSetEntries.

Storage side of UX #3 rides along: plan weights are Double now.
Schema bumps: SplitDocument 2→3, WorkoutDocument 3→4 (a fractional
weight fails an older Int decode, and a rewrite would strip the
irreplaceable actuals), SwiftData cache 4→5. A per-log updatedAt is
reserved for the future cross-device log merge.

Claude-Session: https://claude.ai/code/session_01HJDQQDA9QdP8zByg43H5v3

Workouts/Views/Exercises/ExerciseAddEditView.swift

@@ -41,7 +41,9 @@ struct ExerciseAddEditView: View {
         self.exercise = exercise
         self.split = split
 
-        let w = exercise.weight
+        // The tens/ones pickers step whole values; a fractional stored weight
+        // shows (and saves back) its whole part until UX #3's UI lands.
+        let w = Int(exercise.weight)
         _exerciseName = State(initialValue: exercise.name)
         _loadType = State(initialValue: exercise.loadTypeEnum)
         _minutes = State(initialValue: exercise.durationMinutes)
@@ -200,7 +202,7 @@ struct ExerciseAddEditView: View {
             doc.exercises[idx].name = exerciseName
             doc.exercises[idx].sets = sets
             doc.exercises[idx].reps = reps
-            doc.exercises[idx].weight = newWeight
+            doc.exercises[idx].weight = Double(newWeight)
             doc.exercises[idx].loadType = loadType.rawValue
             doc.exercises[idx].durationSeconds = durationSecs
             // ON → a (possibly empty) array; OFF → nil, discarding any prior settings.