fix: Build frontend package before publishing to npm

The package was shipping raw JSX (main: src/index.jsx) which webpack in
MFE builds cannot process since babel-loader excludes node_modules by
default.

Follows the same pattern as @openedx/frontend-plugin-framework:
- Use fedx-scripts babel to compile src/ -> dist/ before publishing
- Set main to dist/index.js
- Add files: ["dist"] to publish only compiled output
- Add @openedx/frontend-build as a devDependency for fedx-scripts

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

Author: feanil

.github/workflows/release.yml

@@ -115,6 +115,8 @@ jobs:
 
       - name: Update the package version and publish
         run: |
+          npm install --include=dev
           npm version ${{ needs.release.outputs.version }}
+          npm run build
           npm publish
         working-directory: './frontend'

frontend/package.json

@@ -1,11 +1,18 @@
 {
   "name": "@openedx/sample-plugin",
   "version": "__semantically__released__",
-  "main": "src/index.jsx",
+  "main": "dist/index.js",
+  "files": ["dist"],
   "repository": "https://github.com/openedx/sample-plugin",
+  "scripts": {
+    "build": "fedx-scripts babel src --out-dir dist --source-maps --ignore **/*.test.jsx,**/*.test.js"
+  },
   "peerDependencies": {
     "@edx/frontend-platform": "*",
     "@openedx/paragon": "*",
     "react": "*"
+  },
+  "devDependencies": {
+    "@openedx/frontend-build": "*"
   }
 }