feat(cli): add metadata subcommands for overlay management

- Add 6 subcommands: get, set, clear, diff, import, export
- Connect to gRPC MetadataService
- Support JSON and CSV formats
- All subcommands functional, help output correct

crates/musicfs-cli/Cargo.toml

@@ -14,10 +14,13 @@ musicfs-cache.path = "../musicfs-cache"
 musicfs-cas.path = "../musicfs-cas"
 musicfs-fuse.path = "../musicfs-fuse"
 musicfs-metadata.path = "../musicfs-metadata"
+musicfs-grpc.path = "../musicfs-grpc"
 
 clap.workspace = true
 tokio.workspace = true
 tokio-util.workspace = true
+tokio-stream.workspace = true
+tonic.workspace = true
 tracing.workspace = true
 tracing-subscriber.workspace = true
 tracing-appender.workspace = true
@@ -26,6 +29,8 @@ dirs.workspace = true
 toml.workspace = true
 parking_lot.workspace = true
 libc.workspace = true
+serde.workspace = true
+serde_json.workspace = true
 
 [target.'cfg(target_os = "linux")'.dependencies]
 tracing-journald.workspace = true