feat(materials): add campaign materials overlay for sessions

Let GMs manage and show images over the scene from the editor and control panel, with zoom tools, help docs, and full ru/en i18n.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/main/project/assetPrune.ts

@@ -14,6 +14,7 @@ export function collectReferencedAssetIds(p: Project): Set<AssetId> {
     for (const au of sc.media.audios) refs.add(au.assetId);
   }
   for (const au of p.campaignAudios) refs.add(au.assetId);
+  for (const m of p.materials ?? []) refs.add(m.assetId);
   return refs;
 }