switch to keystone.guru tiles + enemy data

Replaces the upreza-derived 4K dungeon textures + AtlasLoot boss-coord
overlay (which had a consistent positional offset against texture skulls)
with keystone.guru's z=4 tile pyramid stitched to 6144x4096 WebP per floor.

kg's split_floors.js gives per-dungeon enemies, packs (polygons), patrols
(polylines), and map icons calibrated to those tiles, so overlays align
pixel-perfectly. 27/29 classic dungeons now have full enemy/pack data;
ZG + Sunken Temple have maps only.

Pipeline: tools/kg_fetch.py -> tools/kg_stitch.py -> tools/kg_build_data.py.

.gitignore

@@ -14,8 +14,6 @@ Thumbs.db
 *.swp
 
 # Large data assets — not tracked in git (no LFS yet)
-# data/uprez is an 11 GB sparse-clone of upreza interface
-data/uprez/
 # legacy hires PNG dump (gone, but keep ignored)
 data/maps_png_hires/
 # 336 MB of WebP map tiles — exclude until LFS is set up
@@ -23,3 +21,4 @@ web/assets/maps/
 
 # Build output
 output/
+data/kg/