fix: port conflicts and API proxy for Electron dev mode

- Add Vite proxy: /api/* requests from renderer (5173) → Express (3000)
- Add dynamic port finding: if 3000 is taken, auto-pick next available
- Import net module for port checking
- Use dynamic expressPort in production URL loading

electron.vite.config.ts

@@ -67,6 +67,13 @@ export default defineConfig({
     server: {
       hmr: process.env.DISABLE_HMR !== 'true',
       watch: process.env.DISABLE_HMR === 'true' ? null : {},
+      // Proxy API calls to the embedded Express server
+      proxy: {
+        '/api': {
+          target: 'http://127.0.0.1:3000',
+          changeOrigin: true,
+        },
+      },
     },
   },
 });