ci: add workflow to build installable VSIX from feature branches

Runs on every push to non-main branches: lints, packages the extension
with vsce, and uploads the .vsix as a downloadable artifact (14-day retention).

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

Author: njb90

.github/workflows/build-vsix.yml

@@ -0,0 +1,37 @@
+name: Build VSIX
+
+on:
+  push:
+    branches-ignore:
+      - main
+
+jobs:
+  build-vsix:
+    name: Build installable VSIX
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: "20"
+          cache: npm
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Run linting
+        run: npm run lint
+
+      - name: Package extension
+        run: npx vsce package --no-dependencies -o cloudinary-${{ github.ref_name }}.vsix
+
+      - name: Upload VSIX artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: cloudinary-${{ github.ref_name }}
+          path: cloudinary-${{ github.ref_name }}.vsix
+          retention-days: 14