Banner forms stay in sync across project switches and reopens

The cookie banner editor form had a stale-state bug: switching to a different project, or closing and reopening the editor modal, sometimes left the form holding the previous banner's values. You could think you were editing one banner and accidentally save the wrong one.

The form now resets cleanly to the right state on every entry: a project switch loads the banner from the new project, closing the modal discards in-progress edits, and reopening starts from the current persisted state. There is no path left where you can see one project's banner config inside another project's editor.