fix(core): guard material-ref parsers against non-string values (Sentry MONOREPO-EDITOR-EM) (#486)

* fix(core): guard material-ref parsers against non-string values (Sentry MONOREPO-EDITOR-EM)

getLibraryMaterialIdFromRef and getSceneMaterialIdFromRef only guarded
against null/undefined, then called .startsWith(). When a non-string
material ref reaches them (legacy/malformed wall material slot ref),
.startsWith is undefined -> TypeError: e.startsWith is not a function.

Narrow with typeof !== 'string' -> return null, so a bad ref degrades to
'no library/scene material' instead of throwing during wall material
resolution (packages/viewer wall-materials.ts -> parseMaterialRef).

* test(core): cover malformed material refs

---------

Co-authored-by: Aymeric Rabot <aymeric.rabot@gmail.com>

packages/core/src/material-library.test.ts

@@ -0,0 +1,13 @@
+import { describe, expect, test } from 'bun:test'
+import { getLibraryMaterialIdFromRef, getSceneMaterialIdFromRef } from './material-library'
+
+describe('material references', () => {
+  test('rejects malformed runtime values instead of calling string methods', () => {
+    const malformedRefs: unknown[] = [42, true, {}, []]
+
+    for (const ref of malformedRefs) {
+      expect(getLibraryMaterialIdFromRef(ref as string)).toBeNull()
+      expect(getSceneMaterialIdFromRef(ref as string)).toBeNull()
+    }
+  })
+})