fix: 🩹 switched package manager

The main reason reason for this switch is a postcss parsing error of some css classes when using pnpm

src-tauri/tauri.conf.json

@@ -1,8 +1,8 @@
 {
   "$schema": "../node_modules/@tauri-apps/cli/schema.json",
   "build": {
-    "beforeBuildCommand": "pnpm svelte:build",
-    "beforeDevCommand": "pnpm svelte:dev",
+    "beforeBuildCommand": "yarn svelte:build",
+    "beforeDevCommand": "yarn svelte:dev",
     "devPath": "http://localhost:3000",
     "distDir": "../dist"
   },