🚨Refactor tmux_utils.py for robust exception-based error handling🚨

[Rixmerz]

• Replace print-and-return error patterns with proper Python exceptions
• Add comprehensive exception hierarchy (TmuxError, TmuxSessionNotFound, etc.)
• Maintain backward compatibility for monitoring functions
• Addresses issue Refactor tmux_utils.py for Robust, Exception-Based Error Handling #13 requirements for structured error communication

Changes:

• get_tmux_sessions(): Now raises TmuxSessionNotFound/TmuxCommandError instead of returning []
• capture_window_content(): Raises TmuxCaptureError instead of returning error string
• get_window_info(): Raises specific exceptions instead of returning {'error': '...'}
• send_keys_to_window(): Raises exceptions instead of returning False
• send_command_to_window(): Raises exceptions instead of returning False
• Monitoring functions handle exceptions gracefully for backward compatibility

Closes #13

[Rixmerz]

@Jedward23