[Feature]: Watchlist-Personalized Newsletter Digest

[fatherlinux]

Parent

Child of #141 (UX 1.0: Community Platform & Personalization)

Overview

The weekly newsletter digest exists (newsletterDigestService.js, Buttondown integration, PR #376/#373), but it sends the same content to all subscribers. This feature wires subscription data into the digest so users with a watchlist get prioritized content from their followed locations.

Requirements

• If user has followed POIs, prioritize events/news at those locations in their digest
• If user has no follows, fall back to valley-wide highlights (current behavior)
• "Most liked this week" section (depends on Like feature)
• Per-user digest generation (or segmented sends via Buttondown)

Architecture Considerations

• Current digest is a single HTML blob sent to all subscribers
• Personalization requires either:
  • Per-user digest generation + individual sends, OR
  • Buttondown segments/tags based on subscription data
• Start simple: maybe just a "Your followed places" section prepended to the standard digest

Dependencies

• Requires: POI subscriptions (already exists)
• Optional: Like counts (for "most liked" section)
• Newsletter infrastructure already exists (Buttondown, preview cron)