feat: add latency indicator and broadcast target selection

- Added a latency indicator to the status bar, displaying round-trip time for SSH sessions.
- Implemented functionality to select specific sessions for broadcasting input, allowing users to manage broadcast targets.
- Enhanced SFTP functionality with bookmark management, enabling users to bookmark directories and navigate to them easily.
- Introduced a modal for user-defined snippet variables, allowing dynamic command execution with placeholders.
- Added port forwarding management for SSH sessions, including the ability to start and stop port forwards.
- Improved terminal output export functionality, allowing users to download or copy terminal output to clipboard.

internal/api/api.go

@@ -931,6 +931,11 @@ func (s *Service) StopPortForward(sessionID string, forwardID string) error {
 	return s.sessions.StopPortForward(sessionID, forwardID)
 }
 
+// PingSession sends a keepalive request and returns the round-trip time in milliseconds.
+func (s *Service) PingSession(sessionID string) (int64, error) {
+	return s.sessions.PingSession(sessionID)
+}
+
 // ---------------------------------------------------------------------------
 // Session recording
 // ---------------------------------------------------------------------------