fix: add missing build steps in GitHub Actions

- Add React build step before electron-builder
- Copy electron directory to build folder
- Fix 'Application entry file does not exist' error

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: ishikawa-pro

.github/workflows/build-and-release.yml

@@ -38,6 +38,12 @@ jobs:
           sudo apt-get update
           sudo apt-get install -y libnss3-dev libatk-bridge2.0-dev libdrm2 libxcomposite1 libxdamage1 libxrandr2 libgbm1 libxss1 libasound2-dev
           
+      - name: Build React app
+        run: npm run build
+        
+      - name: Copy electron files
+        run: cp -r electron build/
+        
       - name: Rebuild native dependencies
         run: npx electron-rebuild
 

package.json

@@ -1,6 +1,6 @@
 {
   "name": "diff-viewer",
-  "version": "0.1.17",
+  "version": "0.1.18",
   "description": "A rich Git diff viewer with syntax highlighting",
   "main": "build/electron/main.js",
   "homepage": "./",