refactor(JoinDiagnostics, StateDivergence): Consolidate control visibility logic

- Replaced inline control visibility logic in `JoinFailureDiagnosticsPanel` and `StateDivergenceDiagnosticsPanel` with a new method `EnsureMainScrollControlVisible`.
- Improved code readability and maintainability by centralizing the visibility check for controls in the main scroll.

Author: BAKAOLC

Networking/JoinDiagnostics/JoinFailureDiagnosticsPanel.cs

@@ -658,14 +658,26 @@ private void AttachControllerFocusChromeRecursive(Node node)
                 {
                     button.SetMeta(FocusRefreshAttachedMeta, true);
                     button.Pressed += ScheduleFocusRefresh;
-                    button.FocusEntered += () => _mainScroll?.EnsureControlVisible(button);
+                    button.FocusEntered += () => EnsureMainScrollControlVisible(button);
                 }
             }
 
             foreach (var child in node.GetChildren())
                 AttachControllerFocusChromeRecursive(child);
         }
 
+        private void EnsureMainScrollControlVisible(Control control)
+        {
+            var scroll = _mainScroll;
+            if (scroll == null ||
+                !IsInstanceValid(scroll) ||
+                !IsInstanceValid(control) ||
+                !scroll.IsAncestorOf(control))
+                return;
+
+            scroll.EnsureControlVisible(control);
+        }
+
         private void ScheduleFocusRefresh()
         {
             if (_focusRefreshScheduled)

Networking/StateDivergence/StateDivergenceDiagnosticsPanel.cs

@@ -795,14 +795,26 @@ private void AttachControllerFocusChromeRecursive(Node node)
                 {
                     button.SetMeta(FocusRefreshAttachedMeta, true);
                     button.Pressed += ScheduleFocusRefresh;
-                    button.FocusEntered += () => _mainScroll?.EnsureControlVisible(button);
+                    button.FocusEntered += () => EnsureMainScrollControlVisible(button);
                 }
             }
 
             foreach (var child in node.GetChildren())
                 AttachControllerFocusChromeRecursive(child);
         }
 
+        private void EnsureMainScrollControlVisible(Control control)
+        {
+            var scroll = _mainScroll;
+            if (scroll == null ||
+                !IsInstanceValid(scroll) ||
+                !IsInstanceValid(control) ||
+                !scroll.IsAncestorOf(control))
+                return;
+
+            scroll.EnsureControlVisible(control);
+        }
+
         private void ScheduleFocusRefresh()
         {
             if (_focusRefreshScheduled)