chore(release): gate users-branch features for hotfix

Add USERS_BRANCH_FEATURES_ENABLED (off by default) to hide Players library, session tokens, and related UI while keeping the preview import fix. Restore primary Run button when the flag is off.

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

app/main/protocol/dndAssetProtocol.ts

@@ -81,7 +81,7 @@ async function serveFile(info: ReadInfo, request: Request): Promise<Response> {
 export function registerDndAssetProtocol(
   projectStore: ZipProjectStore,
   tokensStore: TokensStore,
-  playersStore: PlayersStore,
+  playersStore: PlayersStore | null,
 ): void {
   session.defaultSession.protocol.handle('dnd', async (request) => {
     const url = new URL(request.url);
@@ -95,7 +95,7 @@ export function registerDndAssetProtocol(
     } else if (url.hostname === 'token') {
       info = tokensStore.getImageReadInfo(asTokenId(id));
     } else if (url.hostname === 'player') {
-      info = playersStore.getImageReadInfo(asPlayerId(id));
+      info = playersStore?.getImageReadInfo(asPlayerId(id)) ?? null;
     }
     if (!info) {
       return new Response(null, { status: 404 });