Add support for creating posts in Discord forum channels (type 15).
Forum channels require a message object when creating threads, unlike
regular threads that are created from existing messages.
Changes:
- Added 'message' parameter to DiscordThreadCreate type
- Updated createThreadDiscord to handle forum posts with message body
- Modified thread-create action to accept and pass message parameter
- Forum posts use direct endpoint: /channels/{channelId}/threads
Usage:
message({
action: "thread-create",
channelId: "<forum_channel_id>",
threadName: "Post Title",
message: "Post content"
})
Fixes: Forum posts previously failed with 'This field is required' error
