feat(train): a workout keeps its plan's steps as laps, shown on its page (ADR 0030, D43)

As a recording with a plan is saved, each step run becomes a lap in the
workout's sealed payload: the step, its round, when it started and ended,
its moving time and distance, with the highest heart rate the zones ran
with. The page lists the steps with their pace, speed or split, stroke
rate, watts and heart rate, marks whether each held its target, and the
charts shade the work steps.

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_de.arb

@@ -83,6 +83,9 @@
   "workoutClimb": "Aufstieg",
   "workoutClimbValue": "{metres} m",
   "workoutSplits": "Abschnitte",
+  "workoutSteps": "Schritte aus {plan}",
+  "workoutOnTarget": "Im Ziel",
+  "workoutOffTarget": "Neben dem Ziel",
   "workoutSplitKm": "km {number}",
   "workoutSplitFiveKm": "{from}–{to} km",
   "workoutPaceChart": "Tempo",