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

README.md

@@ -41,8 +41,13 @@ your own iCloud Drive.
 - **Machine comfort settings** — machine-based exercises remember your setup
   (seat height, back-rest position, pin position, …), shown on the workout
   screen and editable mid-workout; changes save back to the split for next time.
+- **Per-set actuals** — every completed set is recorded automatically with its
+  planned reps and weight, and the rest and finish pages offer a small adjust
+  pill to correct what you actually did (in 2.5 lb / 1.25 kg steps) without
+  breaking the flow; the completed-exercise page shows the recorded sets.
 - **Progress tracking** — weight-progression charts per exercise across past
-  sessions.
+  sessions, plotting the top-set weight you actually lifted; workout volume
+  sums the recorded sets too.
 - **Apple Watch companion** — starting a workout on the iPhone launches the watch
   app straight into it. The watch lists your in-progress workouts; pick one, pick an
   exercise, and run it as a paged flow: a **Ready?** lead-in, count-up work phases,