Fix: Replace attachment file IDs when copying markdown files

[pbirrer]

📝 Summary

When copying markdown files, the attachment IDs embedded in the file content were not updated to match the newly created attachments. This PR fixes that by:

• Updating AttachmentService::copyAttachments() to return a map of old to new file IDs.
• Adding AttachmentService::replaceAttachmentFileIds() to update these references in the file content.

🏁 Checklist

• Code is properly formatted (npm run lint / npm run stylelint / composer run cs:check)
• Sign-off message is added to all commits
• Tests (unit, integration and/or end-to-end) passing and the changes are covered with tests
• Documentation (README or documentation) has been updated or is not required

[rvjr]

@mejo- this is a bugfix we discovered during our internal use of #6676. Copied files still referenced attachments in the attachments folder of the source file, when they were referred in md by file id.

[max-nextcloud]

Thanks a lot for bringing this up and addressing it right away. 🥇

I have one comment. Please check if I'm mistaken - just read the code and did not try it myself.

As I said in the comment... a unit test might come in handy to ensure the function works as desired. If you need further help with writing it let me know.

[max-nextcloud]

I think this will drop the trailing / as it's included in the patterns but not in the replacements.

As this is a public static method and the arguments are not very complex it seems like a good candidate for a unit test. You'd have to mock getContent and putContent on target similarly to how it's done in the testReplaceAttachmentFolderId test.

[max-nextcloud]

Ahh... my bad... the / is ending the regexp. Unit test would still be nice - but now i see that this probably works well as is.

[pbirrer]

Alright, I added a unit test for replaceAttachmentFileIds. It actually helped catch a couple issues with my original regex too.

[mejo-]

Thanks so much for taking care of this @pbirrer! Much appreciated 🫶

[mejo-]

/backport to stable31

[mejo-]

/backport to stable30

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