fix: explicitly attach new windows to existing tab group

openWindow creates the window before tabbingIdentifier is set, so macOS
automatic tabbing doesn't group them. Use addTabbedWindow to explicitly
attach new windows to the connection's existing tab group.

Author: datlechin

TablePro/AppDelegate+WindowConfig.swift

@@ -239,15 +239,25 @@ extension AppDelegate {
             let existingIdentifier = NSApp.windows
                 .first { $0 !== window && isMainWindow($0) && $0.isVisible }?
                 .tabbingIdentifier
-            window.tabbingIdentifier = TabbingIdentifierResolver.resolve(
+            let resolvedIdentifier = TabbingIdentifierResolver.resolve(
                 pendingConnectionId: pendingId,
                 existingIdentifier: existingIdentifier
             )
+            window.tabbingIdentifier = resolvedIdentifier
             configuredWindows.insert(windowId)
 
             if !NSWindow.allowsAutomaticWindowTabbing {
                 NSWindow.allowsAutomaticWindowTabbing = true
             }
+
+            // Explicitly attach to existing tab group — automatic tabbing
+            // doesn't work when tabbingIdentifier is set after window creation.
+            if let existingWindow = NSApp.windows.first(where: {
+                $0 !== window && isMainWindow($0) && $0.isVisible
+                    && $0.tabbingIdentifier == resolvedIdentifier
+            }) {
+                existingWindow.addTabbedWindow(window, ordered: .above)
+            }
         }
     }