fix: prevent Enter key from inserting newline before submit

[hakonharnes]

When the cursor is in the middle of text (e.g., "hello (cursor) world") and pressing Enter to submit, the message would be sent as "hello \nworld" instead of "hello world". This happens because the React onKeyDown handler on EditorContent fires after Tiptap has already processed the Enter key and inserted a newline.

This PR moves the Enter key handling to Tiptap's handleKeyDown in editorProps, which intercepts keystrokes before the editor processes them.

[vercel]

Someone is attempting to deploy a commit to the cgoinglove's projects Team on Vercel.

A member of the Team first needs to authorize it.