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/WatchAppDelegate.swift

@@ -0,0 +1,28 @@
+//
+// WatchAppDelegate.swift
+// Workouts Watch App
+//
+// Copyright 2025 Rouslan Zenetl. All Rights Reserved.
+//
+
+import SwiftUI
+import WatchKit
+import HealthKit
+
+/// Bridges watchOS lifecycle into the workout session. When the phone starts a workout
+/// it calls `startWatchApp(toHandle:)`; watchOS launches (or foregrounds) this app and
+/// delivers the configuration to `handle(_:)`, where we start a session to claim
+/// foreground runtime. The session manager is shared with the view tree via the
+/// environment (see `WorkoutsWatchApp`).
+@MainActor
+final class WatchAppDelegate: NSObject, WKApplicationDelegate {
+    let sessionManager = WorkoutSessionManager()
+
+    func applicationDidFinishLaunching() {
+        sessionManager.requestAuthorization()
+    }
+
+    func handle(_ workoutConfiguration: HKWorkoutConfiguration) {
+        sessionManager.start(with: workoutConfiguration)
+    }
+}