Size Discover button to widest label to prevent layout shift

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

Author: sebgod

src/TianWen.UI.Gui/VkEquipmentTab.cs

@@ -517,7 +517,7 @@ private void RenderDeviceList(
             // [Discover] button at the bottom of the list area
             var discoverBtnY = y + h - buttonH - padding;
             var discoverLabel = State.IsDiscovering ? "Discovering..." : "Discover";
-            var discoverBtnW = _renderer.MeasureText(discoverLabel.AsSpan(), fontPath, fontSize).Width + padding * 4f;
+            var discoverBtnW = _renderer.MeasureText("Discovering...".AsSpan(), fontPath, fontSize).Width + padding * 4f;
             var discoverBtnX = x + padding;
 
             FillRect(discoverBtnX, discoverBtnY, discoverBtnW, buttonH, CreateButton);