Fix persona selection grid to use 2x2 layout for consistency

Changed the Select Participants grid from 3 columns to 2 columns on large screens to match the visual pattern used elsewhere in the platform.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/components/FocusGroupModerator.tsx

@@ -2081,7 +2081,7 @@ Controls how much time GPT-5 spends thinking before responding
                         <Loader2 className="h-8 w-8 animate-spin text-primary" />
                       </div>
                     ) : filteredPersonas.length > 0 ? (
-                      <div className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-3 gap-4">
+                      <div className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-2 gap-4">
                         {filteredPersonas.map((persona) => {
                           // Ensure we have a valid ID (use MongoDB _id if available)
                           const personaId = persona._id || persona.id;