Update watcher to pass None for file_id in FileRemoved events

Watcher doesn't have access to file_id; indexer handles fallback
via metadata lookup or remove_by_path

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/claude-agent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

musicfs/crates/musicfs-sync/src/watcher.rs

@@ -122,7 +122,7 @@ impl OriginWatcher {
                 }
                 EventKind::Remove(_) => {
                     debug!("File removed: {:?}", relative);
-                    event_bus.publish(Event::FileRemoved { path: vpath });
+                    event_bus.publish(Event::FileRemoved { path: vpath, file_id: None });
                 }
                 EventKind::Modify(_) => {
                     debug!("File modified: {:?}", relative);