feat(map-editor): v0.2.0a — Rev 4 layout reorg + mode switch + cheatsheet

Layout (per design paper §11):
 - Top toolbar with Mode buttons (Auto-Tile / Direct), Save, Erase,
   Rotate, Help.
 - Right Layers side-panel (8 rows, top-down draw order) as single
   source of truth for visibility + active layer — replaces the old
   left-edge layer chips.
 - Bottom status bar.

State + actions:
 - mode = "auto-tile" | "direct" (Tab toggles).
 - cheatsheet_open modal toggle (I key, dimmed overlay + key/action
   table).
 - SPOREL_CI=1 auto-exits after 30 frames (matches vagrant pattern;
   ci_frames in manifest is not engine-enforced for kind:"module").

Paint behaviour itself is unchanged from 0.1.0 — bottom palette + the
real Auto-Tile / Direct paint loops land in 0.2.0b/c/d.

deps: lib-core.maps 0.5.1 -> 0.5.2 (consumes set_vertex / get_vertex).

manifest.module

@@ -1,6 +1,6 @@
 {
     "id": "map-editor",
-    "version": "0.1.0",
+    "version": "0.2.0a",
     "kind": "module",
     "api": "^0.1",
     "ci_frames": 30,
@@ -9,7 +9,7 @@
         "fa_terrain_v1": "lib-asset.prototype-fa-starter"
     },
     "deps": [
-        {"id":"lib-core.maps","version":"0.5.1"},
+        {"id":"lib-core.maps","version":"0.5.2"},
         {"id":"lib-core.render","version":"0.1.0"},
         {"id":"lib-core.camera","version":"0.3.0"},
         {"id":"lib-core.input","version":"0.4.0"},