migrate to Vue3

.kilocode/rules/brief.md

@@ -0,0 +1,18 @@
+# Brief
+
+Upgrade all depedencies to a more modern stack:
+
+- node 20,
+- pnpm,
+- vite,
+- vueJS 3.5,
+  - TypeScript 5.8,
+  - eslint and prettier,
+  - pinia for state management with persistence support,
+  - Vue component with setup,
+    - remove `@vue/composition-api` plugin
+- vite-plugin-pwa.
+
+Keep `spotify-player.js`.
+
+Use a step by step approach and a way to check each step works before moving to the next one.