Delete empty untitled chat on navigate-away from ChatView

Previously the empty-conversation cleanup only fired when switching
between chats (convId watcher). Navigating to /notes, /tasks, etc.
left orphaned untitled empty conversations. onUnmounted now runs the
same check, deleting the current conversation if message_count === 0.

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

frontend/src/views/ChatView.vue

@@ -476,6 +476,13 @@ function onGlobalKeydown(e: KeyboardEvent) {
 
 onUnmounted(() => {
   document.removeEventListener("keydown", onGlobalKeydown);
+  // Clean up empty conversation when navigating away from the chat view entirely
+  if (prevConvId) {
+    const conv = store.conversations.find((c) => c.id === prevConvId);
+    if (conv && conv.message_count === 0) {
+      store.deleteConversation(prevConvId);
+    }
+  }
 });
 </script>