feat(cache): fix lazy PK metadata resolution and playlist track ordering

- In `track_metadata.rs`, implement fallback logic for lazy PKs: first try real_pk, then fallback to lazy_pk for metadata keys seeded before download.
- In `db.rs`, add debug logging after migration to track remaining metadata under lazy_pk.
- In `source.rs` (Qobuz):
  - Detect and repair playlists with missing cache entries by forcing refresh when `items.len() < total`.
  - Preserve original track order after parallel processing by attaching and sorting on original index.
  - Handle missing performer/cover gracefully with warnings and provider fallback.
- In `metadata_cache.rs` (Radio France), simplify logging and improve test coverage for expiration logic.
- In `cache.rs`, add debug/warning logs when metadata or cover seeding fails during lazy caching.

pmosource/src/cache.rs

@@ -328,6 +328,7 @@ impl SourceCacheManager {
             None
         };
 
+        let metadata_is_some = metadata.is_some();
         let mut final_metadata = metadata;
         if final_metadata.is_none() {
             if let Some(data) = provider_data.as_ref() {
@@ -352,10 +353,25 @@ impl SourceCacheManager {
 
         if let Some(meta) = final_metadata.as_ref() {
             self.seed_audio_metadata(lazy_pk, meta);
+        } else {
+            #[cfg(feature = "server")]
+            tracing::warn!(
+                "cache_audio_lazy_with_provider: no metadata to seed for {} \
+                 (meta_hint={}, provider_data={})",
+                lazy_pk,
+                metadata_is_some,
+                provider_data.as_ref().map(|d| d.metadata.is_some()).unwrap_or(false)
+            );
         }
 
         if let Some(cover_pk) = final_cover_pk {
             let _ = self.set_audio_metadata(lazy_pk, "cover_pk", json!(cover_pk));
+        } else {
+            #[cfg(feature = "server")]
+            tracing::debug!(
+                "cache_audio_lazy_with_provider: no cover_pk seeded for {}",
+                lazy_pk
+            );
         }
 
         Ok(lazy_pk.to_string())