feat(pwa-offline): Pinia store + IndexedDB; contexto para cache/eliminación; toasts; compatibilidad PWA offline

- Agrega @pinia/nuxt, idb y store central (stores/music.ts)
- Cacheo manual desde menú contextual y borrado (TrackContextMenu)
- Ícono verde para canciones cacheadas, sin auto-cache al reproducir
- Toasts de feedback (stores/toast.ts, ToastContainer)
- Fallback offline de listado a IndexedDB; fix MUSIC_DIR absoluto en preview/prod
- Ajustes PWA: navigateFallback '/', devOptions, workbox condicional
- Estilos y animación del context menu (tema light/dark, blur fuerte)
- Correcciones de sintaxis y posicionamiento exacto al cursor

server/api/music/[filename].get.ts

@@ -30,9 +30,9 @@ export default defineEventHandler(async (event) => {
     
     // Determine the music directory path
     let musicDir: string
-    if (process.env.MUSIC_DIR) {
-      // If MUSIC_DIR is set, resolve it (handles both absolute and relative paths)
-      musicDir = resolve(process.cwd(), process.env.MUSIC_DIR)
+    if (config.musicDirAbs || process.env.MUSIC_DIR) {
+      // Prefer absolute dir from runtimeConfig; fallback to env (resolved relative to repo root at build time)
+      musicDir = (config.musicDirAbs as string) || resolve(process.cwd(), process.env.MUSIC_DIR!)
     } else {
       // Fallback to public/music
       const defaultPublicPath = config.public?.musicPath || '/music'