feat(web): letter avatars for custom model groups and agents (#31)

Co-authored-by: Alice <alice@prismshadow.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

packages/web/src/components/layout/sidebar.tsx

@@ -417,7 +417,12 @@ export function Sidebar({
                     aria-label={collapsed ? S.nav.expandGroup : S.nav.collapseGroup}
                     className="flex min-w-0 flex-1 items-center gap-1 rounded px-1 py-0.5 text-left transition-colors duration-150 hover:bg-gray-200/50 dark:hover:bg-gray-800/50"
                   >
-                    <AgentAvatar id={agent.agentId} size={18} className="shrink-0 rounded" />
+                    <AgentAvatar
+                      id={agent.agentId}
+                      name={agentDisplayName(agent)}
+                      size={18}
+                      className="shrink-0 rounded"
+                    />
                     <span className="min-w-0 truncate text-xs font-semibold uppercase tracking-wide text-gray-500 dark:text-gray-400">
                       {agentDisplayName(agent)}
                     </span>