Add an Apple Watch face complication that opens the app

A static WidgetKit accessory widget (launcher only — no data sharing,
App Group, or entitlements). Tapping any accessory widget opens its
containing app, so this is enough to place a Workouts button on the
watch face. Supports the circular, corner, inline, and rectangular
accessory families.

New 'Workouts Watch Widget' app-extension target embedded in the watch
app via project.yml.

README.md

@@ -29,6 +29,9 @@ your own iCloud Drive.
   bidirectional: drive from either device — swipe ahead, finish a set, add one — and the
   other follows. Only *human* transitions are sent; automatic ones (a rest timer ending)
   advance both devices independently off shared start times, so they never fight.
+- **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.
 - **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.