Add GitHub Actions

Author: danbarr

.github/actions/setup/action.yaml

@@ -0,0 +1,24 @@
+name: 'Setup Action'
+description: 'Checks out the repo, sets up node, and installs dependencies'
+runs:
+  using: 'composite'
+  steps:
+    - name: Checkout repository
+      uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4
+
+    - name: Set up Node.js
+      uses: actions/setup-node@39370e3970a6d050c480ffad4ff0ed4d3fdee5af # v4
+      with:
+        node-version: '22'
+
+    - name: Cache dependencies
+      id: cache
+      uses: actions/cache@1bd1e32a3bdc45362d1e726936510720a7c30a57 # v4.2.0
+      with:
+        path: ./node_modules
+        key: modules-${{ hashFiles('package-lock.json') }}
+
+    - name: Install dependencies
+      if: steps.cache.outputs.cache-hit != 'true'
+      run: npm ci
+      shell: bash

.github/workflows/_static-checks.yaml

@@ -0,0 +1,41 @@
+name: Static checks
+
+on:
+  workflow_call:
+
+jobs:
+  lint:
+    name: Lint and format checks
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4
+
+      - name: Setup
+        uses: ./.github/actions/setup
+
+      - name: Run ESLint
+        run: npm run eslint
+
+      - name: Run markdownlint
+        uses: DavidAnson/markdownlint-cli2-action@a23dae216ce3fee4db69da41fed90d2a4af801cf # v19
+        with:
+          globs: |
+            **/*.md
+            !node_modules
+
+      - name: Run Prettier
+        run: npm run prettier
+
+  build:
+    name: Build site
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout Repository
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4
+
+      - name: Setup
+        uses: ./.github/actions/setup
+
+      - name: Build site
+        run: npm run build

.github/workflows/on-pr.yaml

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+name: On PR
+
+on:
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  static-checks:
+    name: Static checks
+    uses: ./.github/workflows/_static-checks.yaml
+    secrets: inherit