feat(map-editor): v0.2.0c.3 — debug overlay (D toggle, per-cell slot/rot)

Diagnostic for the dual-grid + blob-14 painting model: D-key toggles
a per-cell text annotation rendered over the map. For each material
cell on the active layer, draws "S<slot>r<rot>" (and "f" when flip=1)
in green at the cell's top-left, sourced from the new lib-core.maps
0.5.5 cell_material_slot getter.

Use case: confirm that the renderer actually picks distinct slots
(corner_full / tee_full / cross / etc.) for painted regions rather
than always picking slot 13 solid — the rectilinear style fills enough
of each cell that visually adjacent slots 3/7/13 are hard to
distinguish without numerical labels.

Inline today; plan-stub
`docs/superpowers/plans/2026-05-29-debug-overlay-extract-to-lib.md`
deferred until a 2nd consumer (vagrant debug-render, puppet-editor,
etc.) appears.

Also bumps lib-core.maps dep 0.5.4 -> 0.5.5.

manifest.module

@@ -1,6 +1,6 @@
 {
     "id": "map-editor",
-    "version": "0.2.0c.2",
+    "version": "0.2.0c.3",
     "kind": "module",
     "api": "^0.1",
     "ci_frames": 30,
@@ -9,7 +9,7 @@
         "blob_rect_stone": "lib-asset.prototype-blob-geom"
     },
     "deps": [
-        {"id":"lib-core.maps","version":"0.5.4"},
+        {"id":"lib-core.maps","version":"0.5.5"},
         {"id":"lib-core.render","version":"0.1.0"},
         {"id":"lib-core.camera","version":"0.3.0"},
         {"id":"lib-core.input","version":"0.4.0"},