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

project.yml

@@ -69,10 +69,12 @@ targets:
       - path: Workouts Watch App
         excludes:
           - "Resources/Info-*.plist"
+          - "Resources/*.entitlements"
     settings:
       base:
         PRODUCT_BUNDLE_IDENTIFIER: dev.rzen.indie.Workouts.watchkitapp
         INFOPLIST_FILE: "Workouts Watch App/Resources/Info-watchOS.plist"
+        CODE_SIGN_ENTITLEMENTS: "Workouts Watch App/Resources/Workouts-watchOS.entitlements"
         GENERATE_INFOPLIST_FILE: false
         SWIFT_STRICT_CONCURRENCY: complete
         WATCHOS_DEPLOYMENT_TARGET: "26.0"