Add HIIT watch runner, rest-time setting, and HealthKit watch auto-launch

- Redesign the watch app into an active-workout runner: a root gate shows the
  in-progress workout's exercises or prompts to start one on iPhone, and each
  exercise runs as a horizontally-paged HIIT cycle (count-up work, count-down
  rest with final-three-second haptics + auto-advance, One More / Done on the
  last set). Replaces the old history list.
- Add a configurable rest-between-sets duration in iPhone Settings (default 45s),
  synced to the watch over WatchConnectivity.
- Launch the watch app into the session when a workout starts on the phone via
  HealthKit (startWatchApp); the watch runs an HKWorkoutSession for foreground
  runtime and ends it when the workout finishes. Adds the HealthKit entitlement +
  Health usage strings on both targets and WKBackgroundModes on the watch.

Claude-Session: https://claude.ai/code/session_018gg69MaUetDNzWzBXisfMV

Workouts Watch App/WorkoutsApp.swift

@@ -11,11 +11,13 @@ import SwiftData
 @main
 struct WorkoutsWatchApp: App {
     @State private var services = WatchAppServices()
+    @WKApplicationDelegateAdaptor(WatchAppDelegate.self) private var appDelegate
 
     var body: some Scene {
         WindowGroup {
             ContentView()
                 .environment(services.bridge)
+                .environment(appDelegate.sessionManager)
                 .modelContainer(services.container)
                 .task { services.activate() }
         }