rename: AI Assistant → HartBOT

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/chat/ChatPanel.tsx

@@ -157,7 +157,7 @@ export default function ChatPanel({ open, onClose, contextType, contextId }: Cha
           onClick={() => setShowSessions((v) => !v)}
           className="flex-1 text-left text-sm font-semibold text-content hover:text-accent transition-colors"
         >
-          AI Assistant
+          HartBOT
         </button>
         <button
           onClick={handleNewChat}