feat: Implement Real-Time Directory Monitoring

[VelkaRepo]

Objective
Transform HashShield from an "On-Demand Scanner" into a "Real-Time Protection System."

Proposed Solution

• Use the watchdog Python library to monitor file system events (CREATE, MODIFY).
• When a new file is detected in a monitored directory (e.g., /Downloads), automatically trigger scan_file_daemon(filepath).

Acceptance Criteria

• Create a new watchdog_service.py module.
• Implement a hashshield --watch <directory> command.
• Ensure low CPU usage during idle times.