Add gRPC Search service with Search and SearchStream RPCs

- Proto definitions for SearchRequest/SearchResponse/SearchResult
- SearchService implementing MusicFs trait
- Query validation (empty check, 256 char max, limit cap at 10k)
- Streaming support via tokio mpsc channel

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

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

musicfs/crates/musicfs-grpc/Cargo.toml

@@ -4,3 +4,16 @@ version.workspace = true
 edition.workspace = true
 
 [dependencies]
+musicfs-search = { path = "../musicfs-search" }
+musicfs-core = { path = "../musicfs-core" }
+tonic.workspace = true
+prost.workspace = true
+tokio.workspace = true
+tokio-stream.workspace = true
+tracing.workspace = true
+
+[build-dependencies]
+tonic-build.workspace = true
+
+[dev-dependencies]
+tempfile.workspace = true