Add document redaction functionality

Is your feature request related to a problem? Please describe.
When scanning sensitive documents, there is often a need to redact (black out) certain parts containing private information like account numbers, addresses, or other personal data before sharing or storing the documents. Currently, users need to use another app to redact sensitive information.

Describe the solution you'd like
Add a redaction tool that allows users to:

• Select areas of the scanned document to be redacted
• Draw black rectangles over sensitive information
• Choose between different redaction styles (black boxes, pixelation, etc.)
• Apply redaction permanently to the PDF/image output

Describe alternatives you've considered

• Export affected pages, edit them in external image editing apps and then reimport them
• Physically covering sensitive parts before scanning

Additional context
This feature would be particularly useful for all documents containing confidential or sensitive information

No files, tests, or entry points are named in the issue. Start by locating the scanned document output and PDF/image processing paths, then determine how area selection and redaction styles fit them. Done means users can select sensitive regions, apply the requested styles, and receive permanently redacted PDF or image output.