fix: disable modulePreload polyfill for Chrome MV3 compatibility

Vite was injecting modulepreload-polyfill.js into the built output, which
Chrome rejected at runtime with: 'A preload for .../modulepreload-polyfill.js
is found, but is not used because it is a cross-world extension resource
mismatch.'

Disabling the polyfill (extension context does not need it — Chrome 110+
supports bare ESM natively) removes the offending chunk entirely.

vite.config.ts

@@ -49,8 +49,12 @@ export default defineConfig({
     },
   ],
   build: {
+    target: 'chrome110',
     outDir: '../dist',
     emptyOutDir: true,
+    modulePreload: {
+      polyfill: false,
+    },
     rollupOptions: {
       input: {
         background: resolve(__dirname, 'src/background/background.js'),