Features
- add daily lead follow-up digest emailer with lastNotifiedAt dedupe
- add FollowUpsSection component with inline add form, mark-done, and overdue styling
- add GET/POST follow-ups API with auth, ownership, and cache invalidation
- add Next follow-up column with overdue and due-soon color cues in table view
- add PATCH/DELETE follow-up API with status transitions and completedAt stamping
- add useLeadFollowUps query and mutation hooks for dialog UI
- include pending follow-ups in GET /api/leads response for board badges
- show overdue and due-soon follow-up badge on board cards
- wire FollowUpsSection into lead edit dialog above email activity
- add lead follow-up cache tag helpers and invalidateLeadFollowUps
- add LeadFollowUp model with FollowUpStatus enum for lead reminder tracking