build(vite): resolve @/ alias in main + preload configs

The four renderer vite configs all resolve "@" to ./src; main and preload
didn't, so any main-reachable file using @/ imports would break the
bundle. Mirror the same alias block in both configs and revert
lib/errors.ts + src/main/* to the project's @/ convention.

js/vite.preload.config.ts

@@ -1,7 +1,13 @@
+import path from "path";
 import { defineConfig } from 'vite';
 import { defineEnv } from './vite.env';
 
 // https://vitejs.dev/config
 export default defineConfig({
+  resolve: {
+    alias: {
+      "@": path.resolve(__dirname, "./src"),
+    },
+  },
   define: defineEnv,
 });