feat(maps): v0.5.4 — atlas_diffuse_handle + atlas_tile_size_px + atlas_tile_uv

Public accessors for palette-like consumers (map-editor 0.2.0c.2)
that need to render real tile thumbnails. All three return nil when
the atlas-idx is out of range, the slot has no tile in the atlas,
or the texture failed to load (headless test env).

atlas_tile_uv resolves the slot via the same `slot_NN_` regex used
internally by the v3 vertex/material render path, so callers see
the same slot -> tile_id mapping the renderer uses.

manifest.lib

@@ -1 +1 @@
-{"id":"lib-core.maps","version":"0.5.3","api_min":"0.1"}
+{"id":"lib-core.maps","version":"0.5.4","api_min":"0.1"}