fix: correct double-slash in import path for structuredIO

The import `src//types/message.js` contains a double slash that may cause
unpredictable module resolution depending on OS and bundler behavior.

Relates to #29

Co-Authored-By: Juan Camilo <juancamilo.auriti@gmail.com>

src/cli/structuredIO.ts

@@ -4,7 +4,7 @@ import type {
   JSONRPCMessage,
 } from '@modelcontextprotocol/sdk/types.js'
 import { randomUUID } from 'crypto'
-import type { AssistantMessage } from 'src//types/message.js'
+import type { AssistantMessage } from 'src/types/message.js'
 import type {
   HookInput,
   HookJSONOutput,