test: clear CS0219 warnings (assigned-but-unused locals)

Three tests computed a local that was never used:
- VT100MachineBypassTests: removed the dead foundC1 scan loop (the comment
  already explains it is intentionally not an assertion; the real check is
  against the host buffer).
- ScrollablePanelBorderTests: dropped the unused childClicked handler (the
  test only verifies ProcessMouseEvent does not throw on a bordered panel).
- TabControlTests.TabCloseRequested_DoesNotAutoRemove: assert the subscribed
  closeRequested stays false (adding a closable tab must not fire a close),
  alongside the existing tab-count assertion.

Test project now builds warning-clean.

Author: nickprotop

SharpConsoleUI.Tests/Controls/ScrollablePanelBorderTests.cs

@@ -436,9 +436,7 @@ public void Mouse_WithBorder_ClickInsideContent_RoutesToChild()
 		panel.BorderStyle = BorderStyle.Rounded;
 		panel.Padding = new Padding(1, 0, 1, 0);
 
-		bool childClicked = false;
 		var btn = ContainerTestHelpers.CreateButton("Click Me");
-		btn.Click += (_, _) => childClicked = true;
 		panel.AddControl(btn);
 
 		var (system, window) = ContainerTestHelpers.CreateTestEnvironment();

SharpConsoleUI.Tests/Controls/TabControlTests.cs

@@ -1614,8 +1614,9 @@ public void TabCloseRequested_DoesNotAutoRemove()
 		bool closeRequested = false;
 		tab.TabCloseRequested += (_, e) => closeRequested = true;
 
-		// Even if close is requested externally, tab should not be auto-removed
-		// (the event consumer must call RemoveTab)
+		// Adding a closable tab must not spontaneously request a close, and tabs are never
+		// auto-removed — the event consumer is responsible for calling RemoveTab.
+		Assert.False(closeRequested);
 		Assert.Equal(2, tab.TabCount);
 	}
 

SharpConsoleUI.Tests/Security/VT100MachineBypassTests.cs

@@ -39,23 +39,10 @@ public void VT100Machine_C1CsiViaUtf8_ReachesScreenBuffer()
 			var vt = new VT100Machine(40, 5);
 			vt.Process(payload);
 
-			// Check if U+009B ended up in any cell
-			bool foundC1 = false;
-			for (int x = 0; x < 40; x++)
-			{
-				var cell = vt.Screen.GetCell(x, 0);
-				if (cell.Character.Value >= 0x0080 && cell.Character.Value <= 0x009F)
-				{
-					foundC1 = true;
-					break;
-				}
-			}
-
-			// If the VT100Machine consumed the CSI internally (processed it as
-			// a real CSI sequence and applied SGR), then no C1 in cells — the
-			// sequence was handled. If it stored the raw C1 char, that's the vuln.
-			//
-			// Either way, verify no C1 controls reach the host buffer via CopyFrom:
+			// The VT100Machine may consume the CSI internally (processed as a real CSI sequence
+			// and SGR applied) or store the raw C1 char — either is acceptable on the screen
+			// buffer. What matters is the security boundary: verify no C1 controls reach the
+			// host buffer via CopyFrom.
 			var hostBuffer = new CharacterBuffer(40, 5);
 			hostBuffer.CopyFrom(vt.Screen, new LayoutRect(0, 0, 40, 5), 0, 0);