Sitemap Visualizer API

GET  /health
GET  /api/boards?limit=100&offset=0
POST /api/boards       { slug?, title?, state }
GET  /api/boards/:slug
PUT  /api/boards/:slug { title?, state? }
DELETE /api/boards/:slug

Viewer:
GET /visualizer/               (static editor)
GET /visualizer/:slug          (loads board via API)