Add register_audio_cache/register_cover_cache functions to pmoupnp

Fix "PlaylistManager not initialized" error in play_and_cache example.
The error occurred because pmoplaylist's WriteHandle calls
pmoupnp::get_audio_cache() to validate cache pks, but the global
cache registry wasn't initialized.

Changes:
- Add register_audio_cache() and register_cover_cache() functions
- Export them from pmoupnp lib.rs
- Call them in play_and_cache example after creating caches

This mirrors how UpnpServer initializes the cache registry.

pmoupnp/src/cache_registry.rs

@@ -157,6 +157,44 @@ pub fn get_audio_cache() -> Option<Arc<AudioCache>> {
     CACHE_REGISTRY.read().unwrap().audio_cache()
 }
 
+/// Enregistre le cache audio global
+///
+/// Cette fonction doit être appelée au démarrage de l'application
+/// pour rendre le cache audio disponible globalement.
+///
+/// # Examples
+///
+/// ```rust,ignore
+/// use pmoupnp::cache_registry::register_audio_cache;
+/// use pmoaudiocache::Cache as AudioCache;
+/// use std::sync::Arc;
+///
+/// let audio_cache = Arc::new(AudioCache::new("./cache", 1000)?);
+/// register_audio_cache(audio_cache);
+/// ```
+pub fn register_audio_cache(cache: Arc<AudioCache>) {
+    CACHE_REGISTRY.write().unwrap().set_audio_cache(cache);
+}
+
+/// Enregistre le cache de couvertures global
+///
+/// Cette fonction doit être appelée au démarrage de l'application
+/// pour rendre le cache de couvertures disponible globalement.
+///
+/// # Examples
+///
+/// ```rust,ignore
+/// use pmoupnp::cache_registry::register_cover_cache;
+/// use pmocovers::Cache as CoverCache;
+/// use std::sync::Arc;
+///
+/// let cover_cache = Arc::new(CoverCache::new("./covers", 100)?);
+/// register_cover_cache(cover_cache);
+/// ```
+pub fn register_cover_cache(cache: Arc<CoverCache>) {
+    CACHE_REGISTRY.write().unwrap().set_cover_cache(cache);
+}
+
 /// Construit l'URL complète pour une couverture
 ///
 /// Fonction globale qui utilise le registre de caches pour construire l'URL.

pmoupnp/src/lib.rs

@@ -16,7 +16,9 @@ pub mod variable_types;
 use std::sync::RwLock;
 use std::{collections::HashMap, sync::Arc};
 
-pub use crate::cache_registry::{get_audio_cache, get_cover_cache};
+pub use crate::cache_registry::{
+    get_audio_cache, get_cover_cache, register_audio_cache, register_cover_cache,
+};
 pub use crate::object_trait::*;
 pub use crate::upnp_server::UpnpServerExt;