fix(channelbridge): IM 发送过滤 action/narration + <p>拆多气泡 + 0.5-2s 间隔

把回复转发给 IM 适配器(sendReply)时剥掉 <action>/<narration> 动作/内心独白(Web 端
才渲染灰斜体，IM 只能收纯文本)，并按 <p> 段落拆成多条气泡分别发送；多气泡发送间隔
随机 0.5~2s(仅 IM，Web 前端不延迟)。新增 sanitize.go stripNarration/splitBubbles/
bubbleGap + 测试。

internal/services/channelbridge/channelbridge.go

@@ -597,19 +597,38 @@ func (b *Bridge) sendReply(ctx context.Context, in adapter.UnifiedMessage, a ada
 	if a == nil {
 		return fmt.Errorf("channelbridge: no adapter for platform %q", in.Platform)
 	}
-	out := adapter.UnifiedMessage{
-		Platform:    in.Platform,
-		ChannelType: in.ChannelType,
-		ChannelID:   in.ChannelID,
-		GroupID:     in.GroupID,
-		GroupName:   in.GroupName,
-		SenderID:    in.SenderID,
-		Sender:      in.Sender,
-		Content:     text,
-		ContentType: adapter.ContentText,
-		Timestamp:   time.Now().UTC(),
+	// IM channels receive the reply as one or more bubbles: role-play/action/narration
+	// markup (rendered as muted italic on the Web) is stripped, and each <p> paragraph
+	// becomes its own bubble/message (design/17 §2). A reply that was only an action is
+	// dropped rather than sent empty. A multi-bubble reply spaces its sends 0.5-2s apart
+	// so a burst doesn't flood the channel; the Web frontend has no such delay.
+	bubbles := splitBubbles(text)
+	if len(bubbles) == 0 {
+		b.log.Debug("reply has no plain text, skipped", "platform", in.Platform, "channel", in.ChannelID)
+		return nil
 	}
-	return a.SendMessage(ctx, adapter.UnifiedResponse{Messages: []adapter.UnifiedMessage{out}})
+	for i, content := range bubbles {
+		if i > 0 {
+			time.Sleep(bubbleGap())
+		}
+		out := adapter.UnifiedMessage{
+			Platform:    in.Platform,
+			ChannelType: in.ChannelType,
+			ChannelID:   in.ChannelID,
+			GroupID:     in.GroupID,
+			GroupName:   in.GroupName,
+			SenderID:    in.SenderID,
+			Sender:      in.Sender,
+			Content:     content,
+			ContentType: adapter.ContentText,
+			Timestamp:   time.Now().UTC(),
+		}
+		// Each bubble is its own send so the gap lands between messages.
+		if err := a.SendMessage(ctx, adapter.UnifiedResponse{Messages: []adapter.UnifiedMessage{out}}); err != nil {
+			return fmt.Errorf("channelbridge: send bubble #%d of %d: %w", i+1, len(bubbles), err)
+		}
+	}
+	return nil
 }
 
 // adapter returns the registered adapter for a platform name, or nil.