Fix NavigationView mouse click focus and ScrollablePanel scroll-mode-first UX

NavigationView.ProcessMouseEvent now detects which side was clicked and
explicitly calls FocusNavPane/FocusContentPanel before delegating to the
grid. This fixes click-to-focus failures caused by ColumnContainer breaking
the focus notification chain and the nav ScrollablePanel's CanReceiveFocus
returning false when it has no focusable children and doesn't need scrolling.

ScrollablePanel.SetFocus now enters scroll mode (arrow keys scroll, Tab
focuses first child) when the viewport has been laid out and content
overflows. Non-scrollable panels still delegate to the first focusable
child immediately.

Author: nickprotop

SharpConsoleUI/Controls/NavigationView/NavigationView.Input.cs

@@ -44,6 +44,16 @@ public partial class NavigationView
 		/// <inheritdoc/>
 		public bool ProcessMouseEvent(MouseEventArgs args)
 		{
+			// Determine which side was clicked and set focus accordingly.
+			// The grid's own focus tracking can't reliably handle this because
+			// ColumnContainer breaks the focus notification chain (see da664aa).
+			bool clickedNavSide = args.Position.X < _navColumn.ActualWidth;
+			if (clickedNavSide)
+				FocusNavPane();
+			else
+				FocusContentPanel();
+			_hasFocus = true;
+
 			// Delegate to the grid — it handles dispatching to columns and their children
 			return _grid.ProcessMouseEvent(args);
 		}

SharpConsoleUI/Controls/ScrollablePanelControl/ScrollablePanelControl.Input.cs

@@ -276,19 +276,29 @@ public void SetFocus(bool focus, FocusReason reason = FocusReason.Programmatic)
 
 				if (focusableChildren.Any())
 				{
-					// Focus first or last child based on direction
-					_focusedChild = _focusFromBackward
-						? focusableChildren.Last() as IInteractiveControl
-						: focusableChildren.First() as IInteractiveControl;
+					// If the viewport has been laid out and content overflows, enter scroll
+					// mode first so the user can browse with arrow keys before pressing Tab
+					// to focus the first child.
+					if (_viewportHeight > 0 && NeedsScrolling())
+					{
+						log?.LogTrace("ScrollPanel.SetFocus: needs scrolling, entering scroll mode (focusable children available via Tab)", "Focus");
+					}
+					else
+					{
+						// Content fits in viewport (or layout not yet computed) — delegate focus to child immediately
+						_focusedChild = _focusFromBackward
+							? focusableChildren.Last() as IInteractiveControl
+							: focusableChildren.First() as IInteractiveControl;
 
-					log?.LogTrace($"ScrollPanel.SetFocus: delegating to child {_focusedChild?.GetType().Name} (backward={_focusFromBackward})", "Focus");
+						log?.LogTrace($"ScrollPanel.SetFocus: delegating to child {_focusedChild?.GetType().Name} (backward={_focusFromBackward})", "Focus");
 
-					if (_focusedChild is IFocusableControl fc)
-					{
-						if (_focusedChild is IDirectionalFocusControl dfc)
-							dfc.SetFocusWithDirection(true, _focusFromBackward);
-						else
-							fc.SetFocus(true, reason);
+						if (_focusedChild is IFocusableControl fc)
+						{
+							if (_focusedChild is IDirectionalFocusControl dfc)
+								dfc.SetFocusWithDirection(true, _focusFromBackward);
+							else
+								fc.SetFocus(true, reason);
+						}
 					}
 				}
 				else