Enhance Radio France source with API routes initialization and default album art

This commit enhances the Radio France source by:

1. Updating the main.rs file to clarify the purpose of registering the Radio France source, including API route initialization
2. Modifying sources.rs to:
   - Add RadioFranceExt to the imports
   - Initialize API routes for Radio France after registering the source
3. Updating source.rs to:
   - Use a default logo for Radio France containers when server_base_url is configured
   - Apply the default logo to both group and 'Radios ICI' containers

These changes improve the integration and visual presentation of Radio France content within the media server.

PMOMusic/src/main.rs

@@ -54,7 +54,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         }
     }
 
-    // Enregistrer la source Radio France
+    // Enregistrer la source Radio France (inclut l'initialisation des routes API)
     info!("📻 Registering Radio France source...");
     if let Err(e) = server.write().await.register_radiofrance().await {
         tracing::warn!("⚠️ Failed to register Radio France source: {}", e);