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

Shared/Model/Enums.swift

@@ -81,8 +81,8 @@ enum MetricSource: String, Codable, Sendable {
     case phoneEstimate
 }
 
-/// Display unit for weights. The stored weight values are plain integers and are
-/// never rewritten when this changes — switching only relabels what's shown.
+/// Display unit for weights. The stored weight values are unit-less numbers and
+/// are never rewritten when this changes — switching only relabels what's shown.
 enum WeightUnit: String, CaseIterable, Codable, Sendable {
     case lb
     case kg
@@ -101,6 +101,15 @@ enum WeightUnit: String, CaseIterable, Codable, Sendable {
         }
     }
 
+    /// Render a stored weight value with the current unit's label, trimming a
+    /// trailing ".0" so whole values stay clean: "45 lb", "42.5 kg".
+    func format(_ value: Double) -> String {
+        let text = value.truncatingRemainder(dividingBy: 1) == 0
+            ? String(Int(value))
+            : String(value)
+        return "\(text) \(abbreviation)"
+    }
+
     /// Render a stored weight value with the current unit's label, e.g. "135 lb".
     func format(_ value: Int) -> String { "\(value) \(abbreviation)" }
 }