feat: discuss article in briefing chat via 💬 button on news cards

Clicking 💬 on a news card in the briefing panel pre-fills the briefing
chat input with the article title, snippet, and source so the user can
ask the briefing LLM to summarize or discuss it directly.

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

frontend/src/views/BriefingView.vue

@@ -174,6 +174,15 @@ async function send() {
   }
 }
 
+function discussArticle(item: NewsItem) {
+  const snippet = item.snippet ? `\n\n"${item.snippet.slice(0, 400)}${item.snippet.length > 400 ? '…' : ''}"` : ''
+  input.value = `Can you summarize and discuss this article for me?\n\n**${item.title}**${snippet}\n\nSource: ${item.source}`
+  // Scroll the chat panel into view on narrow layouts
+  nextTick(() => {
+    document.querySelector('.briefing-chat')?.scrollIntoView({ behavior: 'smooth', block: 'nearest' })
+  })
+}
+
 function onKeydown(e: KeyboardEvent) {
   if (e.key === 'Enter' && !e.shiftKey) {
     e.preventDefault()
@@ -525,6 +534,12 @@ onMounted(async () => {
               @click="handleReaction(item.id, 'down')"
               title="Not interested"
             >👎</button>
+            <button
+              v-if="isToday && todayConvId"
+              class="reaction-btn discuss-btn"
+              @click="discussArticle(item)"
+              title="Discuss in briefing chat"
+            >💬</button>
           </div>
         </div>
       </div>