圆桌会商各步接入流式回答速度指示器，复用主聊天 SpeedPill 与全局开关。

新增 DialogueSpeedMeter 与 useDialogueSpeedMetrics，在 Step1/2/3 气泡底部展示 tok/s 与耗时。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend-web/src/components/workspace/messages/message-token-usage.tsx

@@ -23,7 +23,7 @@ function classifySpeed(tps: number): { color: string; label: string } {
   return { color: "#ef4444", label: "缓慢" };
 }
 
-function formatDuration(ms: number): string {
+export function formatDuration(ms: number): string {
   if (ms < 1000) return `${Math.round(ms)} ms`;
   if (ms < 60_000) return `${(ms / 1000).toFixed(1)} s`;
   const mins = Math.floor(ms / 60_000);
@@ -31,7 +31,7 @@ function formatDuration(ms: number): string {
   return `${mins}m ${secs}s`;
 }
 
-function SpeedPill({ metric }: { metric: MessageMetric }) {
+export function SpeedPill({ metric }: { metric: MessageMetric }) {
   const fill = Math.max(0, Math.min(1, metric.tokensPerSec / FULL_SCALE_TOKENS_PER_SEC));
   const { color, label } = classifySpeed(metric.tokensPerSec);
   const display =