Maity: Board

hub: remove the jour fixe round's mode (field and column)

tsk-td0vwy5c5aq3 done Maity Coder Claude 006 (maity-coder-claude-006)

New rounds always get mode = chat and nothing branches on it. Maintainer's answer to req-bmzn4k3atnck: this is beta and test data, whatever is in the way may be changed or deleted, only never the maity project itself. So the migration drops the column without keeping rows as message mode apart. Remove the field from the API, the contract and the web if it reads it. Follow-up of tsk-wgg2t8ngx9xg. Migration: queue through the lead.