feat(exercice): exécution de séance avec module séquence et bips (ticket #60)

Ajoute le lecteur de bips d'étapes (presentation/exercise_step_audio.dart,
port ExerciseStepAudioCuePlayer injectable en test, jamais le vrai
audioplayers en test) et les fichiers audio associés
(assets/audio/step_countdown_short.wav, step_completion_long.wav).
Câble ActiveExerciseStepUseCases dans app_bootstrap.dart et l'expose à
WorkoutExecutionScreen. Les appels audio réels sont protégés par un
try/catch qui log sans jamais bloquer la progression d'étape. flutter
pub get OK (ajout audioplayers), analyze propre (mêmes infos
préexistantes + 2 nouvelles use_build_context_synchronously, non
bloquantes), 100/100 tests verts, build APK debug validé.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

pubspec.lock

@@ -41,6 +41,62 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "2.13.1"
+  audioplayers:
+    dependency: "direct main"
+    description:
+      name: audioplayers
+      sha256: "2ba4bb2944baacbdd5372ff8254a8e7feb8c10d7739545e392f5605a8f618745"
+      url: "https://pub.dev"
+    source: hosted
+    version: "6.8.1"
+  audioplayers_android:
+    dependency: transitive
+    description:
+      name: audioplayers_android
+      sha256: f5ff5b15620fbab8cb0849e9636c48e2b96c3f0f71723bbbe2ad3c761b205f05
+      url: "https://pub.dev"
+    source: hosted
+    version: "5.3.0"
+  audioplayers_darwin:
+    dependency: transitive
+    description:
+      name: audioplayers_darwin
+      sha256: "1ca553add991384ecf421b9569da850f3ab2472ffb83f6970b0416365abc51be"
+      url: "https://pub.dev"
+    source: hosted
+    version: "6.5.0"
+  audioplayers_linux:
+    dependency: transitive
+    description:
+      name: audioplayers_linux
+      sha256: "15178b726b7cdee5364d0463c8d445630c4e0fb7d26612b73c767e7d25de9417"
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.3.0"
+  audioplayers_platform_interface:
+    dependency: transitive
+    description:
+      name: audioplayers_platform_interface
+      sha256: "765f6f0e6dca55cb471c9483fc77700564b3484d19198aca4ebb5147c6c85acb"
+      url: "https://pub.dev"
+    source: hosted
+    version: "7.2.0"
+  audioplayers_web:
+    dependency: transitive
+    description:
+      name: audioplayers_web
+      sha256: ae1e0103c865a03e273f6d13d97b93f5595eac09915729cd5e37ef96e2857319
+      url: "https://pub.dev"
+    source: hosted
+    version: "5.3.0"
+  audioplayers_windows:
+    dependency: transitive
+    description:
+      name: audioplayers_windows
+      sha256: a70ae82bba2dfcb6eb03dd4815d737a2d46d33ea5a96a03f535cfcaac490e413
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.4.1"
   boolean_selector:
     dependency: transitive
     description:
@@ -813,6 +869,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.4.1"
+  synchronized:
+    dependency: transitive
+    description:
+      name: synchronized
+      sha256: "93b153dcb6a26dcddee6ca087dd634b53e38c10b5aa163e8e49501a776456153"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.4.1"
   term_glyph:
     dependency: transitive
     description:
@@ -837,6 +901,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.4.0"
+  uuid:
+    dependency: transitive
+    description:
+      name: uuid
+      sha256: "9b129329f58692f6e6578329498a8fe9fbe98f090beb764ffbb8ee2eadd01dcd"
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.6.0"
   vector_math:
     dependency: transitive
     description: