feat(train): Record has a card for each activity, its Start opening the sheet for it (ADR 0030, D60)

The Record tab shows a card per activity it records, the interval plans
below. A card's Start opens the Record sheet for that activity, which
keeps every other choice; the sheet no longer chooses the activity, and
so offers the plans and routes for it or for any. While a recording is
under way or waits to be saved, the cards wait, the bar leading back.

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/lib/l10n/app_en.arb

@@ -17,9 +17,7 @@
   "aboutTitle": "About Halkyon Train",
 
   "homeRecordHint": "Record one from the Record tab.",
-  "recordAction": "Record",
   "recordBack": "Back to the recording",
-  "recordSheetTitle": "Record a workout",
   "activityRunning": "Running",
   "activityWalking": "Walking",
   "activityHiking": "Hiking",
@@ -723,5 +721,6 @@
   "homeWeekDistance": "Distance",
   "homeWeekWorkouts": "Workouts",
   "homeWeekDuration": "{hours, plural, =0{{minutes} min} other{{hours} h {minutes} min}}",
-  "@homeWeekDuration": {"placeholders": {"hours": {"type": "int"}, "minutes": {"type": "int"}}}
+  "@homeWeekDuration": {"placeholders": {"hours": {"type": "int"}, "minutes": {"type": "int"}}},
+  "recordPlansHeading": "Interval plans"
 }