Feature Request: Support Single File Scan with iPurity CLI

Description:Currently, iPurity CLI scans the entire DCIM folder of an external device (e.g., iPhone) by default. To enhance usability and support more granular scanning, introduce a new command option allowing users to scan a specific file (image/video) located on their local system.

Proposed CLI Commands:
```bash
ipurity external scan # Existing: Scans entire DCIM directory of the external device.
ipurity local # New: Scans the specified local file (image/video).
```
Use Cases:
Quickly verify individual images or videos without scanning entire directories.
Facilitate future enhancements like detailed analysis on single video files.