[Fix] Discord thread replies show broken message references

[roomote-roomote]

​Opened on behalf of @mrubens. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

• Stop adding Discord message_reference payloads to messages posted inside thread channels.
• Preserve inline reply references for messages posted outside threads.
• Cover both behaviors with focused Discord provider tests.

Why this change was made

The Discord provider attached a reply reference whenever replyToMessageId was present and set its channel_id to the outbound destination. For thread posts, callers can pass parent-channel starter or anchor message IDs, so the resulting cross-channel reference points at a message that does not exist in the thread and Discord renders a broken “Message could not be loaded” artifact.

Impact

Discord thread conversations no longer show broken or redundant inline reply cards. Ordinary channel and direct-message replies continue to reference their target message as before.

[roomote-community]

No code issues found. See task

_{Reviewed b99635f}