Introduce publish workflow

.github/workflows/publish.yaml

@@ -0,0 +1,36 @@
+name: Publish Extension
+
+on:
+  workflow_dispatch:
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version-file: '.nvmrc'
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Run tests
+        run: npm test
+
+      - name: Package extension
+        run: npm run package
+
+      - name: Publish to VS Code Marketplace
+        run: npm exec @vscode/vsce publish --packagePath *.vsix
+        env:
+          VSCE_PAT: ${{ secrets.VSCE_PAT }}
+
+      - name: Publish to OpenVSX
+        run: npm exec ovsx publish *.vsix
+        env:
+          OVSX_PAT: ${{ secrets.OVSX_PAT }}