Fix ProxyJump to use correct username from SSH config

ET was using the destination username for ProxyJump connections instead
of the jumphost's username defined in SSH config.

With this SSH config:
  Host telie
    User corona
  Host step
    User anl
    ProxyJump telie

Running 'et step' would incorrectly try 'anl@home.alelec.net' instead
of 'corona@home.alelec.net' for the jumphost connection.

Fix: Parse jumphost SSH config to extract its username, use that for
the -J flag. Fallback to local username if not specified.

Author: pi-anl

src/terminal/TerminalClientMain.cpp

@@ -298,14 +298,15 @@ int main(int argc, char** argv) {
       // Extract hostname from [user@]host[:sshport] format for ET socket
       // connection
       string jumphostName = jumphost;
+      string jumphostUser = "";
+      string jumphostHostPort = jumphost;  // Preserve host[:port] portion
 
       // Strip user@ prefix if present
       size_t atIndex = jumphostName.find("@");
       if (atIndex != string::npos) {
+        jumphostUser = jumphostName.substr(0, atIndex);
         jumphostName = jumphostName.substr(atIndex + 1);
-      } else {
-        // If no user@ prefix, add it to jumphost for SSH
-        jumphost = username + "@" + jumphost;
+        jumphostHostPort = jumphostName;  // host[:port] without user@
       }
 
       // Strip :port suffix if present (SSH port, not ET port)
@@ -314,7 +315,7 @@ int main(int argc, char** argv) {
         jumphostName = jumphostName.substr(0, colonIndex);
       }
 
-      // Resolve jumphost alias to actual hostname via SSH config
+      // Resolve jumphost alias to actual hostname and username via SSH config
       // jumphostName might be a Host alias (e.g., "telie") that needs
       // resolution
       {
@@ -334,6 +335,12 @@ int main(int argc, char** argv) {
           jumphostName = string(jumphostOptions.host);
           SAFE_FREE(jumphostOptions.host);
         }
+        // Extract username from SSH config if not already specified
+        if (jumphostUser.empty() && jumphostOptions.username) {
+          jumphostUser = string(jumphostOptions.username);
+          LOG(INFO) << "Using jumphost username from SSH config: "
+                    << jumphostUser;
+        }
         // Clean up other allocated fields in jumphostOptions
         SAFE_FREE(jumphostOptions.username);
         SAFE_FREE(jumphostOptions.sshdir);
@@ -346,6 +353,17 @@ int main(int argc, char** argv) {
         free(jumphost_home_dir);
       }
 
+      // If still no username, use local username as fallback
+      if (jumphostUser.empty()) {
+        char* localUsernamePtr = ssh_get_local_username();
+        jumphostUser = string(localUsernamePtr);
+        SAFE_FREE(localUsernamePtr);
+      }
+
+      // Reconstruct jumphost with correct username for SSH -J flag
+      // Preserve the original host[:port] format
+      jumphost = jumphostUser + "@" + jumphostHostPort;
+
       socketEndpoint.set_name(jumphostName);
       socketEndpoint.set_port(result["jport"].as<int>());
     } else {