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.

pmocache/src/db.rs

@@ -1137,7 +1137,23 @@ impl DB {
             return Err(Error::QueryReturnedNoRows);
         }
 
-        tx.commit()
+        tx.commit()?;
+
+        // Compter les métadonnées encore sous l'ancien lazy_pk (après migration de l'asset)
+        let meta_under_lazy: i64 = {
+            let conn = self.lock_conn("update_lazy_to_downloaded_meta_check");
+            conn.query_row(
+                "SELECT COUNT(*) FROM metadata WHERE pk = ?1",
+                [lazy_pk],
+                |r| r.get(0),
+            ).unwrap_or(0)
+        };
+        tracing::debug!(
+            "update_lazy_to_downloaded: {} → {} ({} metadata rows still under lazy_pk)",
+            lazy_pk, real_pk, meta_under_lazy
+        );
+
+        Ok(())
     }
 
     /// Recherche une entry par son origin_url