Value/Label Redaction and Restoration

[ibirothe]

This PR introduces reversible redaction for diagram labels to support secure external sharing.

Changes

• Redacts object and edge labels in diagrams and stores their original values in a JSON mapping file
• Restores original label contents using the saved mapping
• Enables removal of confidential information before sharing diagrams with third parties for visual or layout adjustments

PR roadmap:

• Reaction logic and saving map ✅
• Restore logic from loaded map ✅
• Unit test
• Documentation