feat(train): workouts written to Health Connect (ADR 0030, D31)

A Health Connect row in the account sheet opens its screen: Write my
workouts, off until turned on, Health Connect asking as it is. Then
every workout this phone holds is written there (its session with its
pauses and route, heart rate, speed and the rower's watts as samples,
distance and elevation gained), and written again or deleted as it
changes, here or through a sync, and as the app opens. Client IDs come
from the workout's ID, a version counts up with each change; what was
written is kept in the person's health_connect.json, never synced. A
permission taken back in Health Connect turns writing off and says so;
Health Connect's link to Train's rationale opens a screen of its own.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/train/halkyon_train_flutter/pubspec.yaml

@@ -30,6 +30,10 @@ dependencies:
   # The device's half of signing in with OpenID Connect (ADR 0023): the
   # browser that SimpleLogin's sign-in opens, and on Linux and Windows the
   # loopback it comes back to, which the app builds with its name.
+  # Running Health Connect's writes and reads one at a time (a shared package,
+  # ADR 0030, D31).
+  halkyon_core:
+    path: ../../../packages/halkyon_core
   halkyon_oidc_flutter:
     path: ../../../packages/halkyon_oidc_flutter
   halkyon_train_client: