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/SplitDocumentCodableTests.swift

@@ -45,7 +45,7 @@ struct SplitDocumentCodableTests {
         let decoded = try DocumentCoder.decode(SplitDocument.self, from: data)
 
         #expect(decoded == original)
-        #expect(decoded.schemaVersion == 2)
+        #expect(decoded.schemaVersion == 3)
         #expect(decoded.relativePath == "Splits/\(original.id).json")
         #expect(decoded.exercises.first?.machineSettings?.count == 2)
     }
@@ -100,10 +100,11 @@ struct SplitDocumentCodableTests {
 
     /// A v1 split file carrying the since-removed keys (`weightLastUpdated`,
     /// `weightReminderWeeks`, `category`) must still decode — Codable ignores the
-    /// extra keys, and every remaining field is present in old files. Re-stamping
-    /// `schemaVersion` to the current value (what the app does on any rewrite via the
-    /// cache→document mapper) round-trips cleanly at v2.
-    @Test func decodesLegacyV1SplitAndRoundTripsAtV2() throws {
+    /// extra keys, every remaining field is present in old files, and the integer
+    /// `weight` decodes natively into today's `Double`. Re-stamping `schemaVersion`
+    /// to the current value (what the app does on any rewrite via the
+    /// cache→document mapper) round-trips cleanly at the current version.
+    @Test func decodesLegacyV1SplitAndRoundTripsAtCurrent() throws {
         let json = """
         {
             "schemaVersion": 1,
@@ -143,7 +144,7 @@ struct SplitDocumentCodableTests {
         let reData = try DocumentCoder.encode(decoded)
         let reDecoded = try DocumentCoder.decode(SplitDocument.self, from: reData)
         #expect(reDecoded == decoded)
-        #expect(reDecoded.schemaVersion == 2)
+        #expect(reDecoded.schemaVersion == 3)
     }
 
     /// A workout-log file written before `completed` was removed still carries the