Upgrade spine-prototype demo to multi-layer schema-v2 map

Surface + wall layers with entity slot between them. Uses
maps.draw_map_pre_entities and maps.draw_map_post_entities so character
sprites render between surface and wall layers.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

init.lua

@@ -126,7 +126,7 @@ end
 function render(ctx)
     engine.render.clear_color(engine.render.rgb(20, 20, 30))
     camera.begin()
-        r_lib.draw_map()
+        maps.draw_map_pre_entities()
         -- draw sign on top of map
         engine.render.draw_rect(sign.x - 6, sign.y - 6, 12, 12,
             engine.render.rgb(SIGN_R, SIGN_G, SIGN_B))
@@ -142,6 +142,7 @@ function render(ctx)
             engine.render.rgb(PLAYER_R, PLAYER_G, PLAYER_B))
         -- P.3.6: highlights over selected entities (world-space)
         selection.render_highlights()
+        maps.draw_map_post_entities()
     camera.finish()
     -- P.3.6: drag-box overlay (screen-space, after camera.finish)
     selection.render_drag_box()