kill LibraryItem, unify to MediaItem; decouple schedule engine from providers

ADR-0001: MediaItem absorbs LibraryItem fields (provider_id, external_id,
collection_name, collection_type, synced_at, role/MediaRole).
LibraryItem + LibraryItemRow deleted. All ports/adapters/tests updated.

ADR-0002: schedule engine takes LibraryQuery instead of IProviderRegistry.
Algorithmic blocks query library via search(), manual blocks via get_by_id().
get_stream_url removed from engine; provider_registry moved to ScheduleDeps
for playback-time stream URL resolution in application layer.

BlockContent provider_id field removed (meaningless when querying library).

crates/adapters/jellyfin/src/mapping.rs

@@ -1,4 +1,4 @@
-use domain::{ContentType, MediaItem, MediaItemId, MediaItemRow};
+use domain::{ContentType, MediaItem, MediaItemId, MediaItemRow, MediaRole};
 
 use crate::models::JellyfinItem;
 
@@ -17,7 +17,7 @@ pub(crate) fn map_jellyfin_item(item: JellyfinItem) -> Option<MediaItem> {
         .unwrap_or(0);
 
     Some(MediaItem::from_persistence(MediaItemRow {
-        id: MediaItemId::new(item.id),
+        id: MediaItemId::new(&item.id),
         title: item.name,
         content_type,
         duration_secs,
@@ -30,5 +30,11 @@ pub(crate) fn map_jellyfin_item(item: JellyfinItem) -> Option<MediaItem> {
         episode_number: item.index_number,
         thumbnail_url: None,
         collection_id: None,
+        provider_id: String::new(),
+        external_id: item.id,
+        collection_name: None,
+        collection_type: None,
+        synced_at: None,
+        role: MediaRole::default(),
     }))
 }