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 Watch AppTests/WatchHelpersTests.swift

@@ -34,7 +34,7 @@ struct WatchHelpersTests {
 
     private static let ts = Date(timeIntervalSince1970: 1_700_000_000)
 
-    private func log(id: String, sets: Int, reps: Int, weight: Int, loadType: LoadType) -> WorkoutLogDocument {
+    private func log(id: String, sets: Int, reps: Int, weight: Double, loadType: LoadType) -> WorkoutLogDocument {
         WorkoutLogDocument(
             id: id, exerciseName: "Ex-\(id)", order: 0, sets: sets, reps: reps, weight: weight,
             loadType: loadType.rawValue, durationSeconds: 0, currentStateIndex: 0,