Save Project Followup Rules

Apply one follow-up sequence to every campaign in the project, transactionally.

The "apply to all" action for follow-ups (T-372) — per-campaign edits go through PATCH /segments/{id}. One transaction instead of N concurrent client PATCHes (which could partially fail and leave campaigns inconsistent). rules is already clamped by SegmentFollowupRules (max_touches <= 6, delay_days in [1,30]).