chore(slack): declare @types/node explicitly instead of relying on hoisting

The Slack package sets types: ["node"] in its tsconfig but did not declare @types/node, so type resolution depended on workspace hoisting. Declare it at the repo-pinned version, matching the other packages that opt into node types. vitest stays root-provided, consistent with every other package.

Author: ericallam

packages/slack/package.json

@@ -49,6 +49,7 @@
   "devDependencies": {
     "@arethetypeswrong/cli": "^0.18.5",
     "@trigger.dev/sdk": "workspace:4.5.0-rc.7",
+    "@types/node": "^24.13.3",
     "rimraf": "6.0.1",
     "tshy": "^3.0.2",
     "tsx": "4.17.0"