Add a per-user lead agent and make the right pane task-focused

internal/agents/mergetitle_internal_test.go

@@ -39,7 +39,7 @@ func TestSetMergeTitle(t *testing.T) {
 		t.Fatalf("default merge title %q, want the task title: %v", task.MergeTitle, err)
 	}
 
-	m := New(st, DefaultLimits, t.TempDir())
+	m := New(st, DefaultLimits, t.TempDir(), t.TempDir())
 	l := &live{id: "s1", vendor: api.Claude, taskID: "t1", projectID: "p1"}
 	call := func(title string) error {
 		raw, err := json.Marshal(setMergeTitleArgs{Title: title})