Reapply "fix(app): more startup efficiency (#18985)"

This reverts commit cbe1337f24.

packages/app/vite.js

@@ -1,7 +1,10 @@
+import { readFileSync } from "node:fs"
 import solidPlugin from "vite-plugin-solid"
 import tailwindcss from "@tailwindcss/vite"
 import { fileURLToPath } from "url"
 
+const theme = fileURLToPath(new URL("./public/oc-theme-preload.js", import.meta.url))
+
 /**
  * @type {import("vite").PluginOption}
  */
@@ -21,6 +24,15 @@ export default [
       }
     },
   },
+  {
+    name: "opencode-desktop:theme-preload",
+    transformIndexHtml(html) {
+      return html.replace(
+        '<script id="oc-theme-preload-script" src="/oc-theme-preload.js"></script>',
+        `<script id="oc-theme-preload-script">${readFileSync(theme, "utf8")}</script>`,
+      )
+    },
+  },
   tailwindcss(),
   solidPlugin(),
 ]