Fix electron-builder: remove type:module, use vite.config.mts instead

The "type": "module" in package.json caused tsup to emit .cjs files instead
of .js, breaking the electron-builder entry point check. Using .mts extension
for vite config achieves ESM for Vite without affecting the rest of the package.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

package.json

@@ -5,7 +5,6 @@
   "main": "build/main/main/main.js",
   "author": "Sucukdeluxe",
   "license": "MIT",
-  "type": "module",
   "scripts": {
     "dev": "concurrently -k \"npm:dev:main:watch\" \"npm:dev:renderer\" \"npm:dev:electron\"",
     "dev:renderer": "vite",