ci: stamp pre-release version in vsix build

Patch package.json version to <version>-pr.<number> before packaging
so the test vsix is clearly distinguishable from the released version.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: njb90

.github/workflows/build-vsix.yml

@@ -31,6 +31,12 @@ jobs:
         id: branch
         run: echo "name=$(echo '${{ github.head_ref }}' | tr '/' '-')" >> "$GITHUB_OUTPUT"
 
+      - name: Stamp pre-release version
+        run: |
+          BASE=$(node -p "require('./package.json').version")
+          jq ".version = \"${BASE}-pr.${{ github.event.pull_request.number }}\"" package.json > package.tmp.json
+          mv package.tmp.json package.json
+
       - name: Package extension
         run: npx @vscode/vsce package --no-dependencies -o cloudinary-${{ steps.branch.outputs.name }}.vsix