chore(map-editor): bump to v0.3.0; cheatsheet + README sync

Updates the in-editor Cheatsheet to reflect the new G binding and
the Esc cascade; bumps manifest.module and the file header to
v0.3.0; adds a Menu UI section to README.md.

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

README.md

@@ -113,3 +113,21 @@ SPOREL_CI=1 ./Sporel.exe --module=map-editor   # exits with rc=0 after ~0.5 s
 - Design paper: `docs/design/2026-05-28-autotile-blob-styles-design.md`
   §11 in `sporel-meta`
 - Plan: `docs/superpowers/plans/2026-05-28-map-editor-blob-v2.md`
+
+## Menu UI (v0.3.0)
+
+Top toolbar replaced with a seven-category menu bar (File, Edit, View,
+Map, Tools, Window, Help) plus a sticky two-segment Mode-pill on the
+right end. Item types: action, modal, toggle, submenu, separator;
+items can be conditionally disabled. A single-stack modal framework
+hosts the existing Cheatsheet (I) and three new modals: Save As, Map
+Properties (read-only), About. The Esc key cascades modal -> menu ->
+quit.
+
+New Map and Open Map appear in the File menu as disabled placeholders
+pending a v3-aware maps.create and an engine.asset.list_dir in a
+future engine + lib slice.
+
+All previous hotkeys (Tab, S, E, R, H, 0, D, G, I, Esc) continue to
+work; their bindings are documented in the items where applicable
+and in the in-editor Cheatsheet modal.