fix: restructure Elec to match electron-vite expected layout

- Move index.html to src/renderer/ (electron-vite hard requirement)
- Flatten React source to src/ (main.tsx, App.tsx, components/)
- Remove debug red background
- Use @tailwindcss/postcss plugin

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Elec/vite.config.ts

@@ -13,7 +13,6 @@ export default defineConfig({
         preload: {
           input: 'src/preload/index.ts',
         },
-      },
     ]),
   ],
 })