Add tray About menu, sync-on-start, sync lock

- "Ueber" menu item in tray context menu opens About dialog
- New user setting "Beim Start automatisch synchronisieren"
  syncs all enabled profiles once at app startup
- Sync lock prevents concurrent sync runs (timer, manual,
  on-start cannot overlap - second request is skipped)

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

src/StarfaceOutlookSync/UI/MainForm.cs

@@ -22,6 +22,7 @@ namespace StarfaceOutlookSync.UI
         private StatusStrip _statusBar;
         private ToolStripStatusLabel _statusLabel;
         private Timer _autoSyncTimer;
+        private volatile bool _syncRunning = false;
 
         public MainForm()
         {
@@ -38,6 +39,21 @@ namespace StarfaceOutlookSync.UI
                 ShowInTaskbar = false;
                 Visible = false;
             }
+
+            // Beim Start automatisch synchronisieren
+            if (settings.SyncOnStart)
+            {
+                _ = SyncAllProfiles();
+            }
+        }
+
+        private async Task SyncAllProfiles()
+        {
+            var profiles = _profileManager.GetProfiles().Where(p => p.Enabled).ToList();
+            foreach (var profile in profiles)
+            {
+                await RunSync(profile);
+            }
         }
 
         protected override void SetVisibleCore(bool value)
@@ -158,6 +174,7 @@ namespace StarfaceOutlookSync.UI
             if (profiles.Any(p => p.Enabled))
                 _trayMenu.Items.Add("-");
 
+            _trayMenu.Items.Add("Ueber", null, (s, e) => ShowAbout());
             _trayMenu.Items.Add("Beenden", null, (s, e) => ExitApplication());
         }
 
@@ -318,6 +335,13 @@ namespace StarfaceOutlookSync.UI
 
         private async Task RunSync(SyncProfile profile)
         {
+            if (_syncRunning)
+            {
+                SetStatus("Sync laeuft bereits, bitte warten...");
+                return;
+            }
+
+            _syncRunning = true;
             try
             {
                 SetStatus($"Synchronisiere '{profile.Name}'...");
@@ -340,6 +364,10 @@ namespace StarfaceOutlookSync.UI
                     ex.Message, ToolTipIcon.Error);
                 SetStatus($"Fehler: {ex.Message}");
             }
+            finally
+            {
+                _syncRunning = false;
+            }
         }
 
         private void SetStatus(string text)