Rename the [Ee]xts dir to ext (#38852)

**WARNING:** This PR will probably blow up all in-flight PRs

at some point in the early days of CmdPal, two of us created seperate
`Exts` and `exts` dirs. Depending on what the casing was on the branch
that you checked one of those out from, it'd get stuck like that on your
PC forever.

Windows didn't care, so we never noticed.

But GitHub does care, and now browsing the source on GitHub is basically
impossible.

Closes #38081

src/modules/cmdpal/ext/SamplePagesExtension/ExplodeInFiveSeconds.cs

@@ -0,0 +1,50 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Timers;
+using Microsoft.CommandPalette.Extensions;
+using Microsoft.CommandPalette.Extensions.Toolkit;
+
+namespace SamplePagesExtension;
+
+internal sealed partial class ExplodeInFiveSeconds : ListPage
+{
+    private readonly bool _repeat;
+
+    private IListItem[] Commands => [
+      new ListItem(new NoOpCommand())
+           {
+               Title = "This page will explode in five seconds!",
+               Subtitle = _repeat ? "Not only that, I'll _keep_ exploding every 5 seconds after that" : string.Empty,
+           },
+        ];
+
+    private bool shouldExplode;
+    private static Timer timer;
+
+    public ExplodeInFiveSeconds(bool repeat)
+    {
+        _repeat = repeat;
+        Icon = new IconInfo(string.Empty);
+        Name = "Open";
+    }
+
+    public override IListItem[] GetItems()
+    {
+        if (shouldExplode)
+        {
+            _ = Commands[9001]; // Throws
+        }
+        else
+        {
+            timer = new Timer(5000);
+            timer.Elapsed += (object source, ElapsedEventArgs e) => { RaiseItemsChanged(9000); };
+            timer.AutoReset = _repeat; // Keep repeating
+            timer.Enabled = true;
+        }
+
+        shouldExplode = true;
+        return Commands;
+    }
+}