Add Open Heart Protocol for anonymous emoji reactions

Created by: jedmund

Summary

• Add self-hosted Open Heart Protocol API endpoint using Redis INCR for atomic emoji counters, with per-IP rate limiting
• Add reusable HeartButton component with SVG heart icon, localStorage persistence, and accessible markup
• Place heart buttons on universe posts, individual photos (inside the metadata card), and album pages

Test plan

• Click heart on a universe post — fills red, stays filled on refresh
• Click heart on a photo — same behavior, button appears inside metadata card
• Click heart on an album — same behavior
• Heart stays filled after page navigation and return
• Multiple rapid clicks don't send multiple requests (disabled after first click)
• curl -X POST /api/heart/universe/test -d '❤️' → 200 "recorded"
• curl /api/heart/universe/test → {"❤️": 1}