feat(bibliotheque): tags et duplication profonde

Ticket #83 B1-B3 : tags JSON dénormalisés, migration Drift v19, mappings sync, helpers de filtre/suggestions, duplication profonde Program/WorkoutTemplate, tests associés.

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

lib/application/ports.dart

@@ -27,6 +27,13 @@ final class StarterContent {
   final WorkoutTemplate workoutTemplate;
 }
 
+final class TagUsage {
+  const TagUsage({required this.tag, required this.count});
+
+  final String tag;
+  final int count;
+}
+
 enum ProgressionPeriod { fourWeeks, threeMonths, all }
 
 enum ProgressionMeasure { manualScore, stopwatchScore, reps, time }