fix(sync): fix BatchResult.errors type mismatch — backend returns {id,error} objects not strings

ios/ChronoMind/Shared/Cloud/PlatformSyncManager.swift

@@ -417,7 +417,12 @@ struct SyncConflict: Codable {
 struct BatchResult: Codable {
     let synced: [String]
     let conflicts: [SyncConflict]
-    let errors: [String]
+    let errors: [BatchError]
+}
+
+struct BatchError: Codable {
+    let id: String
+    let error: String
 }
 
 // MARK: - Offline Queue