fix: add catch handler for LLM generation promise in narration service

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/llm/narrationService.ts

@@ -77,6 +77,8 @@ export function createNarrationService(llmService: LlmService): NarrationService
             event.isLlmGenerated = true;
             service.onEventUpdated?.(event);
           }
+        }).catch(() => {
+          // LLM generation failed; fallback narration is already set
         });
       }