feat: Preserve embedded media when editing descriptions

[Hinne1]

Problem

When editing an issue description, embedded media (images uploaded directly to the description) are lost because the entire ADF is replaced. These media elements have collection/ID references to Jira's media service that cannot be recreated from the filename alone.

Example of lost media:

{
  "type": "mediaSingle",
  "content": [{
    "type": "media",
    "attrs": {
      "id": "abc-123-media-id",
      "collection": "contentId-12345",
      "type": "file"
    }
  }]
}

Proposed Solution

When editing a description:

1. Fetch the existing description ADF
2. Extract all mediaSingle/media nodes
3. When converting new Markdown to ADF, check for !media[filename] references
4. Match filenames to existing media nodes and preserve their IDs
5. Alternatively, preserve all existing media nodes and append them to the new content

Implementation Notes

• The !media[id] syntax currently expects a media ID, but users don't know these IDs
• Could support !media[filename.png] that looks up the ID from existing description media
• Or automatically append all existing media to the end of updated descriptions

Context

An embedded screenshot in NX-14990 was permanently lost when updating the description with new content.

[Hinne1]

Workaround available: The --append flag added in b0051ca can be used to preserve existing description content (including embedded media) when adding new content:

atl issue edit PROJ-1234 --description "Additional notes" --append

This appends new content to the existing description rather than replacing it, so embedded media is preserved.

The full solution (matching !media[filename] references to existing media IDs) remains open for future implementation.