Cross-platform report generation

[joelst]

Cross platform report generation.

This pull request replaces the previous COM/Windows-only PowerPoint report generation with a cross-platform friendly process. The changes update platform support, PowerPoint requirements, and add troubleshooting guidance for report generation.

Platform and requirements changes:

• Updated prerequisites since the script work on Windows, macOS, and Linux, and that PowerPoint is not required for generating reports or importing findings into Azure DevOps or GitHub.
• Revised the important note to explain that report generation uses OpenXML and is cross-platform with PowerShell 7, and provided instructions for non-Windows platforms to use the -ContentFile parameter due to the file picker being Windows-only.

Usage and troubleshooting improvements:

• Added explicit example commands for running the report script on non-Windows platforms and for specifying output directories.
• Introduced a new "Report generation troubleshooting" section with a table of common symptoms and solutions, and explained the importance of preserving named shapes in PPTX templates.

• Added report generation support for macOS and Linux.
• PowerPoint is no longer required for report generation or importing findings.
• Added instructions for running the report script on non-Windows platforms.
• Included troubleshooting section for common report generation issues.