issue edit --body silently strips inline images from the description and deletes their attachments

## What happens

On Jira Cloud, editing an issue's description with `jira issue edit KEY -b "..."` (or via stdin, or the interactive editor) silently removes any images that were embedded inline in the description. Because the images' `media`/`mediaSingle` nodes are dropped from the new description, Jira Cloud treats the underlying attachments as orphaned and deletes them. No warning is shown, and Jira Cloud offers no restore, so this is unrecoverable data loss.

In my case the referenced attachment afterwards returned `404` and was gone permanently.

## Version

```
jira version 1.7.0 (Homebrew), go1.25.5, darwin
```

Jira Cloud, description stored as ADF.

## Steps to reproduce

1. In the Jira web editor, embed an image inline in an issue's description (this creates an ADF `mediaSingle`/`media` node backed by an attachment).
2. Run: `jira issue edit KEY -b "New description text" --no-input`
3. Open the issue in the browser.

**Expected:** the inline image is preserved, or at minimum a warning that inline media will be lost.

**Actual:** the description is replaced with plain text, the inline image is gone, and the attachment it referenced has been deleted from the issue.

The same loss happens with `echo "..." | jira issue edit KEY --no-input`, and via the interactive editor whenever the description text is changed.

## Root cause

In `internal/cmd/issue/edit/edit.go`, the existing ADF description is translated to Markdown to seed the edit:

```go
originalBody = adf.NewTranslator(adfBody, adf.NewJiraMarkdownTranslator()).Translate()
```

The ADF→Markdown translator has no representation for `media`/`mediaSingle` nodes, so inline images are dropped from `originalBody` before the user ever edits it. On save, the (image-less) body is converted back with `md.ToJiraMD(body)` and sent as the new description. The resulting ADF contains no media nodes, so Jira removes the now-orphaned attachments.

The "keep body as is if there were no changes" guard does not protect against this, because `originalBody` has already lost the images — any real edit produces a description without them.

## Suggested directions

- Detect `media`/`mediaSingle` nodes in the existing description and either preserve them (merge them into the new ADF) or refuse the edit with a clear error unless an explicit `--force` / `--allow-media-loss` flag is passed.
- At minimum, print a prominent warning before overwriting a description that contains inline media, and document the behavior.