Add MCPB maintainers group (#12)

Creates a new mcpb-maintainers team under the steering committee with Joan Xie (joan-anthropic), Adam Jones (domdomegg), and Alex Sklar (asklar) as initial maintainers.

src/config/groups.ts

@@ -45,6 +45,12 @@ export const GROUPS = defineGroups([
     memberOf: ['steering-committee'],
     onlyOnPlatforms: ['github'],
   },
+  {
+    name: 'mcpb-maintainers',
+    description: 'MCPB (Model Context Protocol Bundle) maintainers',
+    memberOf: ['steering-committee'],
+    onlyOnPlatforms: ['github'],
+  },
 
   // SDK Maintainers
   {