docs: replace Jekyll with VitePress documentation site

.github/workflows/codeql.yml

@@ -0,0 +1,37 @@
+name: "CodeQL"
+
+on:
+  push:
+    branches: ["main"]
+  pull_request:
+    branches: ["main"]
+  schedule:
+    - cron: "0 0 * * 1"
+
+permissions:
+  contents: read
+
+jobs:
+  analyze:
+    name: Analyze
+    runs-on: ubuntu-latest
+    permissions:
+      actions: read
+      contents: read
+      security-events: write
+
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
+
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@d77b13a0df3134d64a457ea9003f600b09fa1c8a # v3
+        with:
+          languages: javascript
+
+      - name: Autobuild
+        uses: github/codeql-action/autobuild@d77b13a0df3134d64a457ea9003f600b09fa1c8a # v3
+
+      - name: Perform CodeQL Analysis
+        uses: github/codeql-action/analyze@d77b13a0df3134d64a457ea9003f600b09fa1c8a # v3

.github/workflows/docs.yml

@@ -0,0 +1,86 @@
+name: Docs
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - 'docs/**'
+      - '.github/workflows/docs.yml'
+  pull_request:
+    branches: [main]
+    paths:
+      - 'docs/**'
+      - '.github/workflows/docs.yml'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: pages-${{ github.ref }}
+  cancel-in-progress: false
+
+defaults:
+  run:
+    working-directory: docs
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      pages: write
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
+      - uses: actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e # v6
+        with:
+          node-version: '20'
+          cache: 'npm'
+          cache-dependency-path: docs/package-lock.json
+      - run: npm ci
+      - run: npm run docs:build
+      - uses: actions/upload-pages-artifact@56afc609e74202658d3ffba0e8f6dda462b719fa # v3.0.1
+        with:
+          path: docs/.vitepress/dist
+
+  deploy:
+    if: github.ref == 'refs/heads/main'
+    needs: build
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      pages: write
+      id-token: write
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - uses: actions/deploy-pages@d6db90164ac5ed86f2b6aed7e0febac5b3c0c03e # v4.0.5
+        id: deployment
+
+  link-check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
+      - uses: actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e # v6
+        with:
+          node-version: '20'
+          cache: 'npm'
+          cache-dependency-path: docs/package-lock.json
+      - run: npm ci
+      - run: npm run docs:build
+      - uses: lycheeverse/lychee-action@8646ba30535128ac92d33dfc9133794bfdd9b411 # v2.8.0
+        with:
+          args: >
+            docs/.vitepress/dist
+            --root-dir docs/.vitepress/dist
+            --exclude "^file://"
+            --exclude "opencollective"
+            --exclude "llms"
+            --exclude "node-tap.org"
+            --accept '200..=299,403'
+          fail: true

.prettierignore

@@ -3,7 +3,5 @@ out/
 pkg/
 tmp/
 .sass-cache
-docs/_site/
-docs/js/
-docs/assets/js/
+docs/
 vendor

CONTRIBUTING.md

@@ -3,8 +3,7 @@
 There are several ways of contributing to Sinon.JS
 
 - Look into [issues tagged `help-wanted`](https://github.com/sinonjs/sinon/issues?q=is%3Aopen+is%3Aissue+label%3A%22Help+wanted%22)
-- Help [improve the documentation](https://github.com/sinonjs/sinon/tree/master/docs) published
-  at [the Sinon.JS website](https://sinonjs.org). [Documentation issues](https://github.com/sinonjs/sinon/issues?q=is%3Aopen+is%3Aissue+label%3ADocumentation).
+- Help [improve the documentation](https://sinonjs.org) built with [VitePress](https://vitepress.dev). [Documentation issues](https://github.com/sinonjs/sinon/issues?q=is%3Aopen+is%3Aissue+label%3ADocumentation).
 - Help someone understand and use Sinon.JS on [Stack Overflow](https://stackoverflow.com/questions/tagged/sinon)
 - Report an issue, please read instructions below
 - Help with triaging the [issues](https://github.com/sinonjs/sinon/issues). The clearer they are, the more likely they are to be fixed soon.
@@ -106,12 +105,11 @@ To ensure consistent reporting of lint warnings, you should use the same version
 
 ### Tooling
 
-To transparently handle all issues with different tool versions we recommend using [_ASDF: The Multiple Runtime Manager_][asdf]. You would then need the Ruby and Node plugins.
+To transparently handle all issues with different tool versions we recommend using [_ASDF: The Multiple Runtime Manager_][asdf]. You would then need the Node plugin.
 
 <details>
 
 ```
-asdf plugin add ruby
 asdf plugin add nodejs
 asdf install
 ```
@@ -166,3 +164,42 @@ To build run
     $ node build.cjs
 
 The `lib/` directory is generated output. Do not commit it; rebuild it locally with `npm run build` when you need fresh artifacts. The published npm tarball still includes `lib/` via the package allowlist.
+
+## Contributing to documentation
+
+The documentation is built with [VitePress](https://vitepress.dev).
+
+### Local setup
+
+```sh
+cd docs
+npm install
+npm run docs:dev
+```
+
+All docs commands (`docs:build`, `test:docs`, etc.) should be run from the `docs/` directory.
+
+### Build and preview
+
+```sh
+npm run docs:build
+npm run docs:preview
+```
+
+### Testing documentation examples
+
+```sh
+npm run test:docs
+```
+
+### Checking links
+
+Link checking requires [lychee](https://lychee.cli.rs/installation/), which is not installed via npm. Install it separately, then run:
+
+```sh
+npm run docs:link-check
+```
+
+### Deploying
+
+The site is deployed automatically via GitHub Actions when changes are merged to `main`.