chore: upgrade tooling stack

- TypeScript 3.9 -> 5.8
- ESLint 6 -> 9 (flat config)
- Prettier 1 -> 3
- eslint-plugin-vue 6 -> 9
- Add vue-tsc for type checking
- Migrate Sass @import to @use syntax
- Fix Pinia persistence config for v4
- Add Spotify type declarations
- Remove unused registerServiceWorker.ts

vite.config.ts

@@ -128,7 +128,7 @@ export default defineConfig({
   css: {
     preprocessorOptions: {
       scss: {
-        additionalData: `@import "@/styles/variables.scss";`
+        additionalData: `@use "@/styles/variables" as *;`
       }
     }
   },