Memeverse semantic map points

Columnar payload for the /memeverse WebGL map: 16 fixed category "galaxies" (geometry) plus every approved, placed image as a point (parallel arrays — ids as dashless UUID hex, integer x/y world coordinates, a category index, a 0-255 engagement glow byte, and a packed atlas sheet/tile reference or -1 when the point has no baked thumbnail yet). Edge-cached 10 minutes, matching the worker-trending placement cron cadence. No authentication required. Returns 404 while the feature is disabled (MEMEVERSE_ENABLED off); returns 200 with empty arrays before the first layout has ever been computed (frontend renders a "forming" state).