feat(briefing): UI polish for agentic briefing messages

Three visual improvements for the briefing conversation:

1. Intermediate tool-call messages (empty content, briefing_intermediate:
   true) now render as a compact dashed status row with per-tool pills
   showing result counts, instead of an empty assistant bubble followed
   by a stack of ToolCallCards. Click to expand the full cards.

2. Slot badge on non-intermediate briefing messages — "Full Briefing"
   for compilation, "Morning/Midday/Afternoon Update" for slot
   injections. Slot updates get a softer bubble treatment (transparent
   background, muted border, smaller text) so the compilation stays
   visually dominant.

3. Slot separator now triggers on briefing_slot metadata (not the
   compilation-only rss_item_ids), and uses a look-behind so it only
   fires when there's a prior slot message — no separator above the
   first briefing of the day.

New component: BriefingToolStatusRow.vue handles the intermediate
pill row and delegates to ToolCallCard when expanded.

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

frontend/src/components/ChatPanel.vue

@@ -289,6 +289,23 @@ async function send(text: string) {
   await onSubmit({ content: text })
 }
 
+// ── Briefing slot separator helper ────────────────────────────────────────────
+function hasEarlierBriefingSlot(index: number): boolean {
+  const msgs = store.currentConversation?.messages ?? []
+  for (let i = 0; i < index; i++) {
+    const m = msgs[i]
+    const meta = m?.metadata as Record<string, unknown> | null | undefined
+    if (
+      m?.role === 'assistant' &&
+      meta?.briefing_slot != null &&
+      !meta?.briefing_intermediate
+    ) {
+      return true
+    }
+  }
+  return false
+}
+
 defineExpose({ focus, prefill, send })
 </script>
 
@@ -303,13 +320,11 @@ defineExpose({ focus, prefill, send })
             v-for="(msg, index) in store.currentConversation?.messages ?? []"
             :key="msg.id"
           >
-            <!-- Briefing slot separator: shown before a 2nd+ briefing slot message -->
+            <!-- Briefing slot separator: before any non-first slot message (skip intermediate tool-call rows) -->
             <div
-              v-if="briefingMode && index > 0 && msg.role === 'assistant' && msg.metadata?.rss_item_ids"
+              v-if="briefingMode && msg.role === 'assistant' && msg.metadata?.briefing_slot && !msg.metadata?.briefing_intermediate && hasEarlierBriefingSlot(index)"
               class="briefing-slot-separator"
-            >
-              <span>New Briefing Update</span>
-            </div>
+            ></div>
             <ChatMessage
               :message="msg"
               @save-as-note="handleSaveAsNote"
@@ -537,24 +552,10 @@ defineExpose({ focus, prefill, send })
 
 /* Briefing slot separator */
 .briefing-slot-separator {
-  display: flex;
-  align-items: center;
-  gap: 0.75rem;
-  margin: 1.25rem 0 0.5rem;
-  color: var(--color-text-muted, #888);
-  font-size: 0.7rem;
-  font-weight: 600;
-  letter-spacing: 0.08em;
-  text-transform: uppercase;
-  opacity: 0.7;
-}
-.briefing-slot-separator::before,
-.briefing-slot-separator::after {
-  content: '';
-  flex: 1;
   height: 1px;
+  margin: 1.25rem 0 0.75rem;
   background: var(--color-border, #333);
-  opacity: 0.5;
+  opacity: 0.35;
 }
 
 /* Context sidebar */