fix: update offlinedocs/next-env.d.ts to match Next.js 15 output (#22739)

## Problem

`offlinedocs/next-env.d.ts` was committed with content from an older
Next.js version. Next.js 15 rewrites this file on every `next build`
with two changes:

1. Adds `/// <reference path="./.next/types/routes.d.ts" />`
2. Updates the docs URL from `basic-features/typescript` to
`pages/api-reference/config/typescript`

During `make pre-commit` / `make pre-push`, the `pnpm export` step
triggers `next build`, which silently rewrites the file. The
`check-unstaged` guard then detects the diff and fails. If the hook is
interrupted, the regenerated file persists as an unstaged change,
blocking subsequent commits/pushes.

## Fix

Update the committed file to match what the current Next.js 15 produces,
making the build idempotent.

.github/workflows/ci.yaml

@@ -986,6 +986,9 @@ jobs:
         run: |
           make build/coder_docs_"$(./scripts/version.sh)".tgz
 
+      - name: Check for unstaged files
+        run: ./scripts/check_unstaged.sh
+
   required:
     runs-on: ubuntu-latest
     needs: