End the watch session on Discard, plus start-flow UX tweaks

Watch-side follow-through for the End Workout flow:
- The phone now pushes an authoritative set (in-progress, not-started, and
  completed within 24h) instead of the 25 most-recent workouts, and the watch
  prunes any workout absent from it. So a Discard/Delete (or a completed run aging
  out) drops off the watch, empties its active list, and ends the HKWorkoutSession
  — fixing the persistent wrist-raise re-foregrounding. The watch never originates
  a workout, so pruning can't lose local data; the 24h grace keeps a just-finished
  run on screen. The gate pops if the run you're viewing is pruned.

UX tweaks:
- The in-workout ⋯ is now a pull-down Menu (Add Exercise / End Workout) rather than
  an action sheet.
- Starting a split while another workout is still active now prompts to end the
  current one(s) — keeping their progress — or run in parallel. Wired into both
  start paths (the split picker and "Start This Split"), via a shared
  WorkoutDocument.endKeepingProgress() helper.

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

Shared/Model/Documents.swift

@@ -94,6 +94,19 @@ extension WorkoutDocument {
             end = nil
         }
     }
+
+    /// End the workout now, keeping progress: mark every not-completed log as skipped, then
+    /// recompute so it resolves to `.completed` (with `end` stamped). This is the
+    /// "End Workout → Save" operation, shared by the in-workout menu and the
+    /// start-a-new-split prompt.
+    mutating func endKeepingProgress() {
+        for i in logs.indices where (WorkoutStatus(rawValue: logs[i].status) ?? .notStarted) != .completed {
+            logs[i].status = WorkoutStatus.skipped.rawValue
+            logs[i].completed = false
+        }
+        recomputeStatusFromLogs()
+        updatedAt = Date()
+    }
 }
 
 struct WorkoutLogDocument: Codable, Sendable, Equatable, Identifiable {