feat: Implementa gestione intelligente della chiave sorgente con rilevamento PK

- Aggiunge rilevamento automatico Primary Key per connessioni database
- Rimuove completamente il fallback automatico per lato sorgente
- Implementa selezione manuale obbligatoria per file e sorgenti non-DB
- Migliora UI con suggerimenti intelligenti e feedback visivo
- Aggiunge validazione multi-livello (UI, pre-transfer, runtime)
- Introduce metodo GetPrimaryKeyFieldAsync in IDatabaseManager
- Modifica GenerateSourceKey per richiedere sempre campo specifico
- Implementa controllo IsTransferButtonEnabled per validazione form

Breaking changes:
- La generazione automatica delle chiavi sorgente è stata rimossa
- Il campo chiave sorgente è ora obbligatorio quando si usa il sistema associazioni

Fixes: Risolve problema di discovery schema vuoto con selezione database

DataConnection/REST/Implementations/BaseRestServiceClient.cs

@@ -135,6 +135,36 @@ namespace DataConnection.REST.Implementations
             return await CreateEntityAsync(entityName, entityData, cancellationToken);
         }
 
+        public virtual async Task<List<Dictionary<string, object>>> FindEntitiesByKeysAsync(string entityName, Dictionary<string, object> keyFields, CancellationToken cancellationToken = default)
+        {
+            // Default implementation - returns empty list
+            // Derived classes should override this method for service-specific entity search logic
+            await Task.CompletedTask;
+            return new List<Dictionary<string, object>>();
+        }
+
+        public virtual async Task<bool> DeleteEntityAsync(string entityName, string entityId, CancellationToken cancellationToken = default)
+        {
+            // Default implementation - returns false (not supported)
+            // Derived classes should override this method for service-specific entity deletion logic
+            await Task.CompletedTask;
+            return false;
+        }        public virtual async Task<Dictionary<string, object>?> UpdateEntityAsync(string entityName, string entityId, Dictionary<string, object> entityData, CancellationToken cancellationToken = default)
+        {
+            // Default implementation - returns null (not supported)
+            // Derived classes should override this method for service-specific entity update logic
+            await Task.CompletedTask;
+            return null;
+        }
+
+        public virtual async Task<List<Dictionary<string, object>>> FindEntitiesByRequiredFieldsAsync(string entityName, Dictionary<string, object> requiredFields, CancellationToken cancellationToken = default)
+        {
+            // Default implementation - returns empty list (not supported)
+            // Derived classes should override this method for service-specific duplicate detection logic
+            await Task.CompletedTask;
+            return new List<Dictionary<string, object>>();
+        }
+
         public virtual async Task<bool> AuthenticateAsync(CancellationToken cancellationToken = default)
         {
             // Default implementation for basic authentication (already handled in ConfigureHttpClient)