feat: add experimental support for proto3 optional fields in Nginx handler

crates/nxmesh-proto/build.rs

@@ -4,6 +4,7 @@ fn main() -> Result<()> {
     tonic_prost_build::configure()
         .build_server(true)
         .build_client(true)
+        .protoc_arg("--experimental_allow_proto3_optional")
         .compile_protos(&["proto/agent.proto"], &["proto"])?;
     Ok(())
 }