feat(maps): v0.5.2 — set_vertex / get_vertex public APIs

Vertex-grid write/read for the autotile painting path. The map-editor
0.2.0a Auto-Tile mode is the primary consumer; painting a single
vertex causes up to 4 surrounding cells to flip to material via the
any-corner rule. Coordinate-checks reject OOB writes; grid is lazily
allocated on first paint.

manifest.lib

@@ -1 +1 @@
-{"id":"lib-core.maps","version":"0.5.1","api_min":"0.1"}
+{"id":"lib-core.maps","version":"0.5.2","api_min":"0.1"}