Add search/metadata API endpoint

- Add MetadataSearchRequest, SearchResponse, SearchAssetResult,
  SearchAlbumResult, SearchFacet, SearchFacetCount models
- Create SearchApi with SearchMetadataBuilder supporting 35+ filters
- Support filtering by location, dates, camera info, favorites,
  tags, people, albums, text search, and more
- Integrate into Client with client.search().metadata() API

src/apis/mod.rs

@@ -2,11 +2,13 @@
 
 pub mod albums;
 pub mod assets;
+pub mod search;
 pub mod server;
 pub mod timeline;
 
 // Re-export main API modules
 pub use albums::AlbumsApi;
 pub use assets::AssetsApi;
+pub use search::SearchApi;
 pub use server::ServerApi;
 pub use timeline::TimelineApi;