agent: Remove context server settings when uninstalling MCP extension (#32560)

Release Notes:

- agent: Automatically remove context server settings when uninstalling
MCP extension

crates/extension/src/extension_events.rs

@@ -36,6 +36,7 @@ impl ExtensionEvents {
 #[derive(Clone)]
 pub enum Event {
     ExtensionInstalled(Arc<ExtensionManifest>),
+    ExtensionUninstalled(Arc<ExtensionManifest>),
     ExtensionsInstalledChanged,
     ConfigureExtensionRequested(Arc<ExtensionManifest>),
 }