Add debug logging for Starface create/update failures

Log the full request body and response when POST /contacts fails
so we can see why new contacts are not being created.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/StarfaceOutlookSync/Services/SyncEngine.cs

@@ -247,6 +247,7 @@ namespace StarfaceOutlookSync.Services
                                 else
                                 {
                                     // Neu -> in Starface erstellen
+                                    Log($"  Erstelle in Starface: {oc.DisplayName}");
                                     var created = await starface.CreateContactAsync(oc, profile.StarfaceAddressBook);
                                     if (created != null && !string.IsNullOrEmpty(created.StarfaceId))
                                     {
@@ -260,6 +261,11 @@ namespace StarfaceOutlookSync.Services
                                         result.Created++;
                                         Log($"  Erstellt (OL->SF): {oc.DisplayName}");
                                     }
+                                    else
+                                    {
+                                        Log($"  FEHLER: Kontakt konnte nicht erstellt werden: {oc.DisplayName}");
+                                        result.Errors++;
+                                    }
                                 }
                             }
                             catch (Exception ex)