fix: briefing discuss prompt — suppress research tool to prevent full research note

Explicitly instruct the LLM to respond conversationally and not use any
research/search tools when summarizing a shared article excerpt.

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

frontend/src/views/BriefingView.vue

@@ -177,7 +177,7 @@ async function send(overrideText?: string) {
 
 async function discussArticle(item: NewsItem) {
   const snippet = item.snippet ? `\n\n"${item.snippet.slice(0, 400)}${item.snippet.length > 400 ? '…' : ''}"` : ''
-  const text = `Please give me a brief summary and key takeaways for this article (15 sentences or fewer):\n\n**${item.title}**${snippet}\n\nSource: ${item.source}`
+  const text = `Summarize the following article excerpt for me in a few sentences and share your thoughts. Do not use any research or search tools — just respond conversationally based on what I've shared below.\n\n**${item.title}**${snippet}\n\nSource: ${item.source}`
   // Scroll the chat panel into view on narrow layouts, then send
   await nextTick(() => {
     document.querySelector('.briefing-chat')?.scrollIntoView({ behavior: 'smooth', block: 'nearest' })