Save workouts to Apple Health with live watch metrics and a post-workout summary

Watch sessions now run an HKLiveWorkoutBuilder: heart rate and active
energy are collected live (shown in an in-workout HUD), saved to Health
as a real HKWorkout on completion, and carried back to the phone as
WorkoutMetrics on the workout document. Phone-only workouts get an
estimated Health workout (MET x bodyweight x duration) after a 10s
debounce that a late-arriving watch session cancels; a launch sweep
backfills workouts completed within the last day. Dedupe is keyed on
metrics.healthKitWorkoutUUID plus the metrics source.

Splits gain an activity type (strength, functional, HIIT, core, cardio,
cycling) that categorizes the Health workout and picks the MET value.
A post-workout summary sheet (duration, calories, avg/max HR, HR zones,
total volume) fills in live and is also shown on completed workouts.
Weights can now display in lb or kg (display-only relabel), synced to
the watch over the existing application context.

WorkoutDocument schema 1->2 (metrics are irreplaceable, so older apps
must quarantine rather than strip them); cache schema 2 rebuilds the
SwiftData store with the new metric columns. Deleting a workout in the
app intentionally leaves its Health record in place.

README.md

@@ -7,8 +7,9 @@ your own iCloud Drive.
 ## Key Features
 
 - **Workout splits** — organize exercises into reusable routines with custom
-  colors and icons. Start with built-in starter splits (Upper Body / Core /
-  Lower Body) generated from a bundled exercise catalog.
+  colors, icons, and an activity type (strength, HIIT, cardio, …). Start with
+  built-in starter splits (Upper Body / Core / Lower Body) generated from a
+  bundled exercise catalog.
 - **Exercise library** — a bundled catalog of starter exercises (bodyweight and
   machine-based) to populate your splits.
 - **Run a workout** — start a session from a split, then tap an exercise to run it
@@ -34,6 +35,12 @@ your own iCloud Drive.
 - **Watch face complication** — a launcher complication you can place on any Apple
   Watch face; tap it to open the app. Available in the circular, corner, inline, and
   rectangular accessory slots.
+- **Apple Health & Activity rings** — completed workouts are saved to Apple Health
+  and credit your Move and Exercise rings: recorded live on the Apple Watch (heart
+  rate + active energy), or estimated on the iPhone when you train without your
+  watch. See live heart rate and calories on the watch, and a post-workout summary
+  (duration, calories, avg/max heart rate, heart-rate zones, total volume) you can
+  revisit on any past workout. Weights display in your choice of pounds or kilograms.
 - **iCloud Drive sync** — your data lives as human-readable JSON in your iCloud
   Drive, synced across devices and visible in the Files app. iCloud is required.