feat: Add comprehensive visitor retention system
Implemented RSS feeds, newsletter subscriptions, email templates, and admin UI
to encourage repeat visits from self-selected visitors.
## RSS Feeds
- Created RSS 2.0 feed generation (main + topic-specific)
- Endpoints: /feed.xml and /feed/:topic.xml
- Added getPublished() and getPublishedByTag() to BlogPost model
## Newsletter Subscriptions
- Created reusable newsletter modal component
- Added to index, researcher, implementer, leader pages
- Interest selection: research, implementation, governance, project-updates
- Added newsletter trigger button to footer
- Uses existing /api/newsletter/subscribe endpoint
## Email Templates
- Created comprehensive specifications for 4 newsletter tiers
- Research Updates (monthly) - scholarly audience
- Implementation Notes (bi-weekly) - practitioners
- Governance Discussions (sporadic) - stakeholders
- Project Updates (quarterly) - general audience
- Documented template variables, design guidelines
## Admin UI
- Enhanced newsletter management with "Send Newsletter" section
- Tier selection, subject/preview input, JSON content editor
- Preview/test/send buttons (UI ready, email service TBD)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
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