fix: 拆分 RabbitMQ Channel，修复新视频不出现在推荐列表的问题

- RabbitMQ 结构体移除共享 Ch 字段，仅管理 Connection
- 每个MQ组件(Like/Comment/Social/Popularity/Timeline)持有独立 Channel
- Timeline Consumer 使用独立 Channel 并加入自动重连机制
- Redis 操作超时从 50ms 调整为 500ms，避免 NACK 循环
- router.go 中 notification 相关逻辑适配新 API

backend/internal/middleware/rabbitmq/popularityMQ.go

@@ -4,10 +4,12 @@ import (
 	"context"
 	"errors"
 	"time"
+
+	amqp "github.com/rabbitmq/amqp091-go"
 )
 
 type PopularityMQ struct {
-	*RabbitMQ
+	ch *amqp.Channel
 }
 
 const (
@@ -29,14 +31,19 @@ func NewPopularityMQ(base *RabbitMQ) (*PopularityMQ, error) {
 	if base == nil {
 		return nil, errors.New("rabbitmq base is nil")
 	}
-	if err := base.DeclareTopic(popularityExchange, popularityQueue, popularityBindingKey); err != nil {
+	ch, err := base.NewChannel()
+	if err != nil {
 		return nil, err
 	}
-	return &PopularityMQ{RabbitMQ: base}, nil
+	if err := DeclareTopic(ch, popularityExchange, popularityQueue, popularityBindingKey); err != nil {
+		ch.Close()
+		return nil, err
+	}
+	return &PopularityMQ{ch: ch}, nil
 }
 
 func (p *PopularityMQ) Update(ctx context.Context, videoID uint, change int64) error {
-	if p == nil || p.RabbitMQ == nil {
+	if p == nil || p.ch == nil {
 		return errors.New("popularity mq is not initialized")
 	}
 	if videoID == 0 || change == 0 {
@@ -52,5 +59,5 @@ func (p *PopularityMQ) Update(ctx context.Context, videoID uint, change int64) e
 		Change:     change,
 		OccurredAt: time.Now().UTC(),
 	}
-	return p.PublishJSON(ctx, popularityExchange, popularityUpdateRK, event)
+	return PublishJSON(ctx, p.ch, popularityExchange, popularityUpdateRK, event)
 }