fix(chat): let backend auto-generate conversation titles

KnowledgeView and WorkspaceView were passing explicit titles
("Knowledge chat", "Project — Workspace") to createConversation(),
which prevented the backend's auto-title generation from firing
(condition: `not conv_title`). Pass no title so the background
title generator names conversations after their first message.

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

frontend/src/views/WorkspaceView.vue

@@ -135,8 +135,7 @@ onMounted(async () => {
 
   if (workspaceConvId === null) {
     // Create a new workspace conversation and persist its ID
-    const title = project.value ? `${project.value.title} — Workspace` : "Workspace";
-    const conv = await chatStore.createConversation(title);
+    const conv = await chatStore.createConversation();
     workspaceConvId = conv.id;
     isNewConv = true;
     await chatStore.fetchConversation(conv.id);