Count the Bus asset type in e2e 04

The suite job has been red since 3a52f22 (#325), in the runs for
3a52f22, daeffe0 and d349251. Each time e2e 04 failed the same two
checks: every asset type offered once in the + menu, and every type
there with its icon. #325 added the asset type Bus, and the module
still expected 30 types.

- ASSET_TYPE_COUNT is now 31, one per entry of ASSET_TYPES. The menu
  itself was right: each type once, each category sorted, every icon
  there.

Tests:
- e2e 04 (melektaus-atx): ALL PASSED, 63 checks.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/e2e/04-assets.mjs

@@ -2,7 +2,7 @@ import { colourDistance } from '../lib/harness.mjs';
 import { pickAssetType } from './lib/scaffold.mjs';
 
 /** One per entry of `ASSET_TYPES` – a new asset type counts here too. */
-const ASSET_TYPE_COUNT = 30;
+const ASSET_TYPE_COUNT = 31;
 /** The categories of the asset panel and the `+` menu, in their order (`ASSET_CATEGORIES`). */
 const CATEGORIES = ['Basics', 'Visuals', 'Logics', 'Physics', 'Audio'];