fix: use createRequire instead of import attributes for JSON import

Avoids Node version compatibility issues with `with { type: "json" }`
(Node 22+) vs `assert { type: "json" }` (deprecated, errors on Node 22+).
Uses the same createRequire pattern already established in const.ts and
server.ts.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: raman325

src/lib/introspect/message_handler.ts

@@ -1,10 +1,13 @@
+import { createRequire } from "node:module";
 import { UnknownCommandError } from "../error.js";
-import incomingMessageSchema from "../generated/incoming_message_schema.json" with { type: "json" };
 import { MessageHandler } from "../message_handler.js";
 import { IntrospectCommand } from "./command.js";
 import { IncomingMessageIntrospect } from "./incoming_message.js";
 import { IntrospectResultTypes } from "./outgoing_message.js";
 
+const require = createRequire(import.meta.url);
+const incomingMessageSchema = require("../generated/incoming_message_schema.json");
+
 export class IntrospectMessageHandler implements MessageHandler {
   async handle(
     message: IncomingMessageIntrospect,