Implement musicfs-search crate with tantivy index and fuzzy queries

- SearchIndex with Arc<RwLock<IndexWriter>> pattern
- Fuzzy query support via custom term~N parsing
- Indexer with EventBus integration and MetadataLookup trait
- SearchQueryBuilder for programmatic query construction
- remove_by_path fallback for FileRemoved handling

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

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

musicfs/crates/musicfs-search/src/lib.rs

@@ -1 +1,7 @@
-#![allow(dead_code)]
+mod index;
+mod indexer;
+mod query;
+
+pub use index::{SearchError, SearchHit, SearchIndex};
+pub use indexer::{Indexer, IndexerHandle, MetadataLookup};
+pub use query::SearchQueryBuilder;