Improvements to the Cyber-Lenin Web Chat Interface

- Ensure that the real-time generation process of answers is output stably
- Improve visibility by displaying the currently used tool whenever a tool (e.g., web search, internal document lookup) is used during the answer generation process
- Fix a bug where an error occurs due to timeout if an answer takes more than 2 minutes
- Switch the web chat model from DeepSeek v4 Pro to Flash, sacrificing a bit of quality but significantly improving response speed