feat: 升级 session/redis.go 日志为 trace-aware

替换 logger.Log 为 trace.FromContext(ctx)：
- CreateWithID: session 创建日志
- Get: session 获取日志（新增错误日志）
- UpdateConfig: 配置更新日志
- UpdateTitle: 标题更新日志
- GetHistory: 无效历史条目警告日志
- Destroy: session 销毁日志

backend/internal/session/redis.go

@@ -10,8 +10,8 @@ import (
 	"github.com/google/uuid"
 	"github.com/redis/go-redis/v9"
 
-	"github.com/hhs/camtalk/internal/logger"
 	"github.com/hhs/camtalk/internal/models"
+	"github.com/hhs/camtalk/internal/trace"
 	"github.com/hhs/camtalk/internal/util"
 )
 
@@ -88,7 +88,8 @@ func (m *RedisManager) CreateWithID(ctx context.Context, id string, userID strin
 		return "", fmt.Errorf("redis create session: %w", err)
 	}
 
-	logger.Log.Debugw("redis session created", "session", id, "user_id", userID)
+	log := trace.FromContext(ctx)
+	log.Debugw("redis session created", "session_id", id, "user_id", userID)
 	return id, nil
 }
 
@@ -97,8 +98,11 @@ const placeholderHistoryMark = "__placeholder__"
 
 // Get 获取会话。
 func (m *RedisManager) Get(ctx context.Context, sessionID string) (*models.Session, error) {
+	log := trace.FromContext(ctx)
+
 	vals, err := m.rdb.HGetAll(ctx, metaKey(sessionID)).Result()
 	if err != nil {
+		log.Errorw("redis get session failed", "session_id", sessionID, "error", err)
 		return nil, fmt.Errorf("redis get session: %w", err)
 	}
 	if len(vals) == 0 {
@@ -116,6 +120,7 @@ func (m *RedisManager) Get(ctx context.Context, sessionID string) (*models.Sessi
 	sess.Config.DetailLevel = vals["config.detail_level"]
 	sess.Config.Language = vals["config.language"]
 
+	log.Debugw("redis session retrieved", "session_id", sessionID)
 	return sess, nil
 }
 
@@ -151,7 +156,9 @@ func (m *RedisManager) UpdateConfig(ctx context.Context, sessionID string, patch
 
 	// 刷新 TTL
 	m.rdb.Expire(ctx, metaKey(sessionID), m.ttl)
-	logger.Log.Debugw("redis session config updated", "session", sessionID)
+
+	log := trace.FromContext(ctx)
+	log.Debugw("redis session config updated", "session_id", sessionID)
 	return nil
 }
 
@@ -171,7 +178,9 @@ func (m *RedisManager) UpdateTitle(ctx context.Context, sessionID string, title
 	}
 
 	m.rdb.Expire(ctx, metaKey(sessionID), m.ttl)
-	logger.Log.Debugw("redis session title updated", "session", sessionID, "title", title)
+
+	log := trace.FromContext(ctx)
+	log.Debugw("redis session title updated", "session_id", sessionID, "title", title)
 	return nil
 }
 
@@ -286,8 +295,9 @@ func (m *RedisManager) GetHistory(ctx context.Context, sessionID string, limit i
 		}
 		var msg models.Message
 		if err := json.Unmarshal([]byte(raw), &msg); err != nil {
-			logger.Log.Warnw("invalid history entry",
-				"session", sessionID,
+			log := trace.FromContext(ctx)
+			log.Warnw("invalid history entry",
+				"session_id", sessionID,
 				"raw_len", len(raw),
 				"raw_preview", util.Truncate(raw, 100))
 			continue
@@ -440,7 +450,8 @@ func (m *RedisManager) Destroy(ctx context.Context, sessionID string) error {
 		m.rdb.SRem(ctx, userSessKey(userID), sessionID)
 	}
 
-	logger.Log.Debugw("redis session destroyed", "session", sessionID)
+	log := trace.FromContext(ctx)
+	log.Debugw("redis session destroyed", "session_id", sessionID)
 	return nil
 }