Implement NAPI connect() function — single SSH channel as duplex stream

- Add WraithConnectOptions struct with napi fields: server, peer, transport,
  identity (string path or Buffer), tlsServerName, insecure, irohRelay, proxy
- Add WraithStream napi class wrapping SSH channel read/write halves via
  ChannelStream::into_stream() + tokio::io::split()
- Implement connect() async function: transport creation (tcp, tls), SSH client
  connection, authenticate, open direct_tcpip channel, return WraithStream
- Identity field accepts file path (string) or in-memory key data (Buffer)
- All Rust errors marshalled to JavaScript exceptions with descriptive messages
- Add ForwardError enum to wraith-core (required by forward.rs)
- Enable tls, iroh features on wraith-core dependency
- 7 unit tests for key source resolution and address parsing

crates/wraith-core/src/error.rs

@@ -60,6 +60,22 @@ pub enum ConfigError {
     IncompatibleOptions,
 }
 
+#[derive(Debug, thiserror::Error)]
+pub enum ForwardError {
+    #[error("invalid forward spec: {spec}")]
+    InvalidSpec { spec: String },
+    #[error("bind failed")]
+    BindFailed {
+        #[source]
+        source: io::Error,
+    },
+    #[error("channel open failed")]
+    ChannelOpenFailed {
+        #[source]
+        source: Box<dyn std::error::Error + Send + Sync>,
+    },
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;