feat: add prompts/list_changed notification

Add a notification type that servers can use to inform clients when their list of available prompts has changed, similar to the existing notifications for tools and resources. This allows clients to stay in sync with the server's prompt offerings without polling.

schema/schema.ts

@@ -494,6 +494,13 @@ export interface PromptArgument {
   required?: boolean;
 }
 
+/**
+ * An optional notification from the server to the client, informing it that the list of prompts it offers has changed. This may be issued by servers without any previous subscription from the client.
+ */
+export interface PromptListChangedNotification extends Notification {
+  method: "notifications/prompts/list_changed";
+}
+
 /* Tools */
 /**
  * Sent from the client to request a list of tools the server has.
@@ -771,7 +778,8 @@ export type ServerNotification =
   | LoggingMessageNotification
   | ResourceUpdatedNotification
   | ResourceListChangedNotification
-  | ToolListChangedNotification;
+  | ToolListChangedNotification
+  | PromptListChangedNotification;
 
 export type ServerResult =
   | EmptyResult