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

WorkoutsTests/SeedReconcilePlannerTests.swift

@@ -13,7 +13,7 @@ struct SeedReconcilePlannerTests {
     // MARK: - Fixtures
 
     private func exercise(
-        name: String, order: Int = 0, sets: Int = 3, reps: Int = 10, weight: Int = 100
+        name: String, order: Int = 0, sets: Int = 3, reps: Int = 10, weight: Double = 100
     ) -> ExerciseDocument {
         ExerciseDocument(
             id: "EX-\(name)-\(order)", name: name, order: order, sets: sets, reps: reps,