feat: Implement directory validation and shell command quoting

- Added is_valid_directory function to validate directory paths, ensuring they do not contain control characters and are within a specified length.
- Introduced quote_shell_arg to safely quote shell arguments, preventing command injection.
- Created uild_cd_command to generate a command for changing directories in a shell.
- Enhanced the LoginHandler to utilize a login rate limiter, preventing brute-force attacks by tracking failed login attempts.
- Implemented an EncodingCache to optimize encoding detection for SSH connections.
- Updated the UI to include an input field for specifying an initial directory upon login, with appropriate validation and hints.
- Added a quickbar in the terminal interface for easy access to copy and paste functionality.
- Introduced a toast notification system to provide feedback on copy actions.
- Refactored connection storage to encrypt passwords at rest, improving security.
- Updated various templates and styles to accommodate new features and improve user experience.