feat(online): partage client - use cases, inbox cache et import local (ticket #66)

Ajoute l'adapter API distant de partage (infrastructure/remote/share_api.dart)
et les use cases associés (application/use_cases.dart), avec cache
d'inbox et import local des ressources partagées acceptées. Étend le
modèle Drift (migration schemaVersion 11→12) et les entités du domaine
en conséquence. flutter pub get OK, build_runner OK, dart format
appliqué, analyze propre (mêmes infos préexistantes), 124/124 tests
verts, build APK debug validé.

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

lib/domain/entities.dart

@@ -16,6 +16,14 @@ enum SetResultStatus { completed, skipped }
 
 enum ActiveScoreStopwatchStatus { running, stopped }
 
+enum ShareResourceType { program, workoutTemplate }
+
+enum ShareInboxStatus { pending, accepted, declined, revoked }
+
+enum PendingShareActionType { send, accept, decline, revoke }
+
+enum PendingShareActionStatus { pending, succeeded, failed }
+
 enum ActiveExerciseStepProgressStatus {
   notStarted,
   waitingManual,
@@ -154,6 +162,115 @@ final class UserAccountSession {
   }
 }
 
+final class ShareInboxItem {
+  ShareInboxItem({
+    required String shareId,
+    required String senderUserId,
+    required this.resourceType,
+    required String payloadJson,
+    required this.status,
+    required this.createdAt,
+    this.respondedAt,
+  }) : shareId = _nonBlank(shareId, 'Share id'),
+       senderUserId = _nonBlank(senderUserId, 'Sender user id'),
+       payloadJson = _nonBlank(payloadJson, 'Share payload JSON');
+
+  final String shareId;
+  final String senderUserId;
+  final ShareResourceType resourceType;
+  final String payloadJson;
+  final ShareInboxStatus status;
+  final DateTime createdAt;
+  final DateTime? respondedAt;
+
+  ShareInboxItem copyWith({
+    String? senderUserId,
+    ShareResourceType? resourceType,
+    String? payloadJson,
+    ShareInboxStatus? status,
+    DateTime? createdAt,
+    Object? respondedAt = _unchanged,
+  }) {
+    return ShareInboxItem(
+      shareId: shareId,
+      senderUserId: senderUserId ?? this.senderUserId,
+      resourceType: resourceType ?? this.resourceType,
+      payloadJson: payloadJson ?? this.payloadJson,
+      status: status ?? this.status,
+      createdAt: createdAt ?? this.createdAt,
+      respondedAt: respondedAt == _unchanged
+          ? this.respondedAt
+          : respondedAt as DateTime?,
+    );
+  }
+}
+
+final class PendingShareAction {
+  PendingShareAction({
+    required String id,
+    required this.actionType,
+    this.shareId,
+    this.resourceType,
+    this.payloadJson,
+    this.recipientEmailsJson,
+    required this.createdAt,
+    this.lastAttemptAt,
+    this.attemptCount = 0,
+    this.status = PendingShareActionStatus.pending,
+  }) : id = _nonBlank(id, 'Pending share action id') {
+    _requireNonNegative(attemptCount, 'Share action attempt count');
+    if (shareId != null) {
+      _nonBlank(shareId, 'Share id');
+    }
+    if (payloadJson != null) {
+      _nonBlank(payloadJson, 'Share payload JSON');
+    }
+    if (recipientEmailsJson != null) {
+      _nonBlank(recipientEmailsJson, 'Recipient emails JSON');
+    }
+  }
+
+  final String id;
+  final PendingShareActionType actionType;
+  final String? shareId;
+  final ShareResourceType? resourceType;
+  final String? payloadJson;
+  final String? recipientEmailsJson;
+  final DateTime createdAt;
+  final DateTime? lastAttemptAt;
+  final int attemptCount;
+  final PendingShareActionStatus status;
+
+  PendingShareAction copyWith({
+    Object? shareId = _unchanged,
+    ShareResourceType? resourceType,
+    Object? payloadJson = _unchanged,
+    Object? recipientEmailsJson = _unchanged,
+    Object? lastAttemptAt = _unchanged,
+    int? attemptCount,
+    PendingShareActionStatus? status,
+  }) {
+    return PendingShareAction(
+      id: id,
+      actionType: actionType,
+      shareId: shareId == _unchanged ? this.shareId : shareId as String?,
+      resourceType: resourceType ?? this.resourceType,
+      payloadJson: payloadJson == _unchanged
+          ? this.payloadJson
+          : payloadJson as String?,
+      recipientEmailsJson: recipientEmailsJson == _unchanged
+          ? this.recipientEmailsJson
+          : recipientEmailsJson as String?,
+      createdAt: createdAt,
+      lastAttemptAt: lastAttemptAt == _unchanged
+          ? this.lastAttemptAt
+          : lastAttemptAt as DateTime?,
+      attemptCount: attemptCount ?? this.attemptCount,
+      status: status ?? this.status,
+    );
+  }
+}
+
 final class MediaAsset {
   const MediaAsset({
     required this.metadata,