Add minimum height to live panel

Pad running section to 5 lines minimum to prevent panel from
shrinking when fewer tests are running.

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: rogeralsing

src/Asynkron.TestRunner/LiveDisplay.cs

@@ -166,6 +166,7 @@ private IRenderable CreateRunningSection()
     {
         var lines = new List<IRenderable>();
         var textWidth = ContentWidth - 4; // Leave room for status icon and spacing
+        const int minLines = 5; // Minimum lines to prevent panel shrinking
 
         if (_lastCompleted != null && _lastStatus != null)
         {
@@ -190,6 +191,12 @@ private IRenderable CreateRunningSection()
             lines.Add(new Markup("[dim]Waiting for tests...[/]"));
         }
 
+        // Pad to minimum height to prevent flickering
+        while (lines.Count < minLines)
+        {
+            lines.Add(new Text(""));
+        }
+
         return new Rows(lines);
     }