feat(user-agent-auth): add RSA and ECDSA auth key types

Extend user-agent authentication to support Ed25519, ECDSA (secp256k1), and RSA (PSS+SHA-256) with minimal protocol and storage changes. Add key_type to auth requests and useragent_client, update key parsing/signature verification paths, and keep backward compatibility by treating UNSPECIFIED as Ed25519.

server/crates/arbiter-proto/Cargo.toml

@@ -24,6 +24,7 @@ async-trait.workspace = true
 
 [build-dependencies]
 tonic-prost-build = "0.14.3"
+protoc-bin-vendored = "3"
 
 [dev-dependencies]
 rstest.workspace = true

server/crates/arbiter-proto/build.rs

@@ -3,6 +3,11 @@ use tonic_prost_build::configure;
 static PROTOBUF_DIR: &str = "../../../protobufs";
 
 fn main() -> Result<(), Box<dyn std::error::Error>> {
+    if std::env::var("PROTOC").is_err() {
+        println!("cargo:warning=PROTOC environment variable not set, using vendored protoc");
+        let protoc = protoc_bin_vendored::protoc_bin_path().unwrap();
+        unsafe { std::env::set_var("PROTOC", protoc) };
+    }
 
     println!("cargo::rerun-if-changed={PROTOBUF_DIR}");
 
@@ -17,7 +22,6 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
             ],
             &[PROTOBUF_DIR.to_string()],
         )
-        
         .unwrap();
     Ok(())
 }