Add an "End Workout" flow for partially-done workouts

Replace the in-workout "+" toolbar button with an ellipsis menu offering
"Add Exercise" and "End Workout". Ending opens a Save/Discard action sheet:
Save marks the remaining exercises as skipped and resolves the workout to
completed (stamping end), which drops it off the watch's active list and ends
the watch's HealthKit session; Discard soft-deletes it.

Teach the status-from-logs derivation that a skipped log is terminal, and
consolidate the three duplicated copies into a single shared
WorkoutDocument.recomputeStatusFromLogs() so an ended workout stays finished
regardless of which screen the next edit comes from.

Claude-Session: https://claude.ai/code/session_01SCv7zvGFcKy47KSTnTLxRe

Workouts/Views/WorkoutLogs/ExerciseView.swift

@@ -211,21 +211,7 @@ struct ExerciseView: View {
 
     /// Recompute the workout's status/end from its logs.
     private func recomputeWorkoutStatus() {
-        let statuses = doc.logs.map { WorkoutStatus(rawValue: $0.status) ?? .notStarted }
-        let allCompleted = !statuses.isEmpty && statuses.allSatisfy { $0 == .completed }
-        let anyInProgress = statuses.contains { $0 == .inProgress }
-        let allNotStarted = statuses.allSatisfy { $0 == .notStarted }
-
-        if allCompleted {
-            doc.status = WorkoutStatus.completed.rawValue
-            doc.end = Date()
-        } else if anyInProgress || !allNotStarted {
-            doc.status = WorkoutStatus.inProgress.rawValue
-            doc.end = nil
-        } else {
-            doc.status = WorkoutStatus.notStarted.rawValue
-            doc.end = nil
-        }
+        doc.recomputeStatusFromLogs()
     }
 
     /// If the requested log isn't in the working doc yet (just-added race), pull a