[Feature]: Create an ISO image from a folder #632

What would you like Filee to do?

Add folder-to-ISO creation in the app and CLI. The folder’s contents should become the root of the ISO, preserving Unicode filenames and empty directories.

Why / when would you use it?

To package a folder into a data-disc image for mounting, sharing or use with virtual machines, without needing a separate ISO creation tool.

Ideas for how it could work

Following the feedback on #591 and #592:

• Use the in-process, MIT-licensed DiscUtils writer.
• Support ISO 9660 with Joliet only.
• Detect folder inputs in the drag-and-drop and CLI input handling, rather than adding filesystem checks to FormatRegistry.
• Preserve existing destinations if creation fails or is cancelled.
• Report unsupported filenames or file sizes clearly.
• Generate test inputs in code rather than committing third-party sample files.