[Feature] Salesforce: batch describe metadati, discovery parallela e fix scheduler External ID

- Salesforce Composite Batch API per describe SObject: le describe sono ora
  raggruppate in chunk da 25 e inviate come singole POST a /composite/batch,
  riducendo le chiamate API da N a ceil(N/25); per 200 SObject: da 201 a 9 chiamate.

- Discovery entita' REST in parallelo: DiscoverEntitySummariesAsync e
  DiscoverEntitiesAsync avviate simultaneamente; la lista entita' diventa
  interattiva subito dopo le summaries, i dettagli completano in background
  con StateHasChanged() per aggiornare l'UI istantaneamente.

- Fix scheduler - preservazione ExternalIdRelationshipsJson e DefaultValuesJson:
  in DataCoupler.razor.cs entrambi i blocchi di update profilo esistente
  (riattivazione profilo inattivo e sovrascrittura profilo attivo) omettevano
  questi campi nella copia, causandone l'azzeramento silenzioso ad ogni
  re-salvataggio. Ora entrambi i percorsi propagano correttamente i campi JSON.

- Fix scheduler - esclusione campi sorgente External ID dal mapping normale:
  in ScheduledProfileExecutionService.TransformRecordForRest i campi sorgente
  usati nelle External ID Relationships venivano inclusi anche nel loop di
  field mapping standard, generando dati duplicati nell'entita' destinazione.
  Ora il comportamento e' allineato alla UI manuale (TransformRecordToRestEntity).

- Aggiornata documentazione: README.md, AGENTS.md, copilot-instructions.md

Data_Coupler/Services/ScheduledProfileExecutionService.cs

@@ -171,18 +171,25 @@ public class ScheduledProfileExecutionService : IScheduledProfileExecutionServic
                 _logger.LogInformation("Caricate {Count} External ID Relationships dal profilo", externalIdRelationships.Count);
             }
 
+            // 4.6. Parse Default Values
+            var defaultValues = ParseDefaultValues(profile.DefaultValuesJson);
+            if (defaultValues.Any())
+            {
+                _logger.LogInformation("Caricati {Count} default values dal profilo", defaultValues.Count);
+            }
+
             // 5. Determina se utilizzare Salesforce Composite API
             bool useSalesforceComposite = restClient is DataConnection.REST.Implementations.SalesforceServiceClient;
             
             if (useSalesforceComposite)
             {
                 _logger.LogInformation("Utilizzo Salesforce Composite API per il trasferimento");
-                return await ExecuteDataTransferWithCompositeAsync(profile, sourceRecords, restClient, restEntity, restCredential!, fieldMappings, externalIdRelationships, enableDeletionSync);
+                return await ExecuteDataTransferWithCompositeAsync(profile, sourceRecords, restClient, restEntity, restCredential!, fieldMappings, defaultValues, externalIdRelationships, enableDeletionSync);
             }
             else
             {
                 _logger.LogInformation("Utilizzo metodo trasferimento standard per il trasferimento");
-                return await ExecuteDataTransferStandardAsync(profile, sourceRecords, restClient, restEntity, restCredential!, fieldMappings, externalIdRelationships, enableDeletionSync);
+                return await ExecuteDataTransferStandardAsync(profile, sourceRecords, restClient, restEntity, restCredential!, fieldMappings, defaultValues, externalIdRelationships, enableDeletionSync);
             }
         }
         catch (Exception ex)
@@ -417,6 +424,53 @@ public class ScheduledProfileExecutionService : IScheduledProfileExecutionServic
         return relationships;
     }
 
+    /// <summary>
+    /// Parse del JSON dei default values
+    /// </summary>
+    private Dictionary<string, (object? Value, string? Type)> ParseDefaultValues(string? defaultValuesJson)
+    {
+        var defaultValues = new Dictionary<string, (object? Value, string? Type)>();
+        
+        if (string.IsNullOrEmpty(defaultValuesJson))
+        {
+            _logger.LogDebug("DefaultValues JSON è vuoto o null");
+            return defaultValues;
+        }
+
+        _logger.LogDebug("Parsing DefaultValues JSON: {Json}", defaultValuesJson);
+
+        try
+        {
+            var options = new JsonSerializerOptions 
+            { 
+                PropertyNamingPolicy = JsonNamingPolicy.CamelCase 
+            };
+            
+            var deserializedDefaults = JsonSerializer.Deserialize<Dictionary<string, DefaultValueDto>>(defaultValuesJson, options);
+            if (deserializedDefaults != null)
+            {
+                foreach (var entry in deserializedDefaults)
+                {
+                    defaultValues[entry.Key] = (entry.Value.Value, entry.Value.Type);
+                    _logger.LogDebug("Default value: {Field} = {Value} ({Type})",
+                        entry.Key, entry.Value.Value, entry.Value.Type);
+                }
+                
+                _logger.LogInformation("Trovati {Count} default values nel JSON", defaultValues.Count);
+            }
+            else
+            {
+                _logger.LogWarning("Deserializzazione ritornato null per DefaultValues JSON");
+            }
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Errore nel parsing dei default values: {Json}", defaultValuesJson);
+        }
+
+        return defaultValues;
+    }
+
     /// <summary>
     /// Ottiene tutti i record dal database
     /// </summary>
@@ -685,6 +739,7 @@ public class ScheduledProfileExecutionService : IScheduledProfileExecutionServic
         RestEntitySummary restEntity,
         RestApiCredential restCredential,
         Dictionary<string, string> fieldMappings,
+        Dictionary<string, (object? Value, string? Type)> defaultValues,
         List<ExternalIdRelationshipDto> externalIdRelationships,
         bool enableDeletionSync = false)
     {
@@ -699,8 +754,8 @@ public class ScheduledProfileExecutionService : IScheduledProfileExecutionServic
         {
             try
             {
-                // 1. Trasforma il record utilizzando i field mappings e External ID Relationships
-                var restData = TransformRecordForRest(record, fieldMappings, externalIdRelationships);
+                // 1. Trasforma il record utilizzando i field mappings, default values e External ID Relationships
+                var restData = TransformRecordForRest(record, fieldMappings, defaultValues, externalIdRelationships);
 
                 // 2. Gestione associazioni record se abilitata
                 string? entityId = null;
@@ -810,6 +865,7 @@ public class ScheduledProfileExecutionService : IScheduledProfileExecutionServic
         RestEntitySummary restEntity,
         RestApiCredential restCredential,
         Dictionary<string, string> fieldMappings,
+        Dictionary<string, (object? Value, string? Type)> defaultValues,
         List<ExternalIdRelationshipDto> externalIdRelationships,
         bool enableDeletionSync = false)
     {
@@ -820,7 +876,7 @@ public class ScheduledProfileExecutionService : IScheduledProfileExecutionServic
         if (!(restClient is DataConnection.REST.Implementations.SalesforceServiceClient salesforceClient))
         {
             _logger.LogWarning("Client REST non è SalesforceServiceClient, fallback al metodo standard");
-            return await ExecuteDataTransferStandardAsync(profile, sourceRecords, restClient, restEntity, restCredential, fieldMappings, externalIdRelationships, enableDeletionSync);
+            return await ExecuteDataTransferStandardAsync(profile, sourceRecords, restClient, restEntity, restCredential, fieldMappings, defaultValues, externalIdRelationships, enableDeletionSync);
         }
 
         try
@@ -851,7 +907,7 @@ public class ScheduledProfileExecutionService : IScheduledProfileExecutionServic
                     var recordNumber = indexedRecord.RecordNumber;
 
                     // Trasforma il record in base ai mapping e External ID Relationships (operazione locale, thread-safe)
-                    var restData = TransformRecordForRest(record, fieldMappings, externalIdRelationships);
+                    var restData = TransformRecordForRest(record, fieldMappings, defaultValues, externalIdRelationships);
 
                     // Genera la chiave sorgente e l'hash dei dati per questo record (include MAPPING_SIGNATURE)
                     var sourceKey = GenerateSourceKey(record, profile.SourceKeyField);
@@ -1144,12 +1200,30 @@ public class ScheduledProfileExecutionService : IScheduledProfileExecutionServic
     private Dictionary<string, object> TransformRecordForRest(
         Dictionary<string, object> sourceRecord, 
         Dictionary<string, string> fieldMappings,
+        Dictionary<string, (object? Value, string? Type)> defaultValues,
         List<ExternalIdRelationshipDto>? externalIdRelationships = null)
     {
         var restData = new Dictionary<string, object>();
 
+        // Costruisce un set dei campi sorgente usati esclusivamente come External ID Relationship:
+        // questi NON devono essere inviati anche come mapping normale (stessa logica della UI manuale).
+        var externalIdSourceFields = (externalIdRelationships != null)
+            ? externalIdRelationships
+                .Where(r => !string.IsNullOrWhiteSpace(r.SourceField))
+                .Select(r => r.SourceField)
+                .ToHashSet()
+            : new HashSet<string>();
+
+        // 1. Applica field mappings (escludendo i campi sorgente usati per External ID Relationships)
         foreach (var mapping in fieldMappings)
         {
+            // Salta il campo se è usato come sorgente in un External ID Relationship
+            if (externalIdSourceFields.Contains(mapping.Key))
+            {
+                _logger.LogDebug("Campo sorgente '{SourceField}' usato in External ID Relationship, escluso dal mapping normale", mapping.Key);
+                continue;
+            }
+
             if (sourceRecord.ContainsKey(mapping.Key))
             {
                 var value = sourceRecord[mapping.Key];
@@ -1164,7 +1238,22 @@ public class ScheduledProfileExecutionService : IScheduledProfileExecutionServic
             }
         }
 
-        // Aggiungi External ID Relationships (per Salesforce)
+        // 2. Applica default values (solo se il campo non è già stato mappato)
+        foreach (var defaultValue in defaultValues)
+        {
+            if (!restData.ContainsKey(defaultValue.Key))
+            {
+                var (value, type) = defaultValue.Value;
+                if (value != null)
+                {
+                    restData[defaultValue.Key] = value;
+                    _logger.LogDebug("Applicato default value: {Field} = {Value} ({Type})", 
+                        defaultValue.Key, value, type);
+                }
+            }
+        }
+
+        // 3. Aggiungi External ID Relationships (per Salesforce)
         if (externalIdRelationships != null && externalIdRelationships.Any())
         {
             foreach (var relationship in externalIdRelationships)