fix: 修复日志重复输出及清理冗余迁移逻辑

- logger: sinkCore 包装 tee core 时绕过了子 core 的 Check 级别过滤，
  导致每条日志同时写入 stdout 和 stderr，表现为启动日志重复显示。
  修复为正确委托 Check 给内部 tee core，sinkCore.Write 仅负责 sink 转发。
- migration 054: 移除冗余的遗留列回填逻辑，migration 009 已完成数据迁移，
  直接删除遗留列即可。

backend/internal/pkg/logger/logger.go

@@ -351,17 +351,18 @@ func (s *sinkCore) With(fields []zapcore.Field) zapcore.Core {
 }
 
 func (s *sinkCore) Check(entry zapcore.Entry, ce *zapcore.CheckedEntry) *zapcore.CheckedEntry {
-	if s.Enabled(entry.Level) {
-		return ce.AddCore(entry, s)
+	// Delegate to inner core (tee) so each sub-core's level enabler is respected.
+	// Then add ourselves for sink forwarding only.
+	ce = s.core.Check(entry, ce)
+	if ce != nil {
+		ce = ce.AddCore(entry, s)
 	}
 	return ce
 }
 
 func (s *sinkCore) Write(entry zapcore.Entry, fields []zapcore.Field) error {
-	if err := s.core.Write(entry, fields); err != nil {
-		return err
-	}
-
+	// Only handle sink forwarding — the inner cores write via their own
+	// Write methods (added to CheckedEntry by s.core.Check above).
 	mu.RLock()
 	sink := currentSink
 	mu.RUnlock()

backend/migrations/054_drop_legacy_cache_columns.sql

@@ -8,37 +8,7 @@
 --   cache_creation_1h_tokens  (defined in 001_init.sql)
 --
 -- Migration 009 already copied data from legacy → canonical columns.
--- But upgraded instances may still have post-009 writes in legacy columns.
--- Backfill once more before dropping to prevent data loss.
-
-DO $$
-BEGIN
-    IF EXISTS (
-        SELECT 1
-        FROM information_schema.columns
-        WHERE table_schema = 'public'
-          AND table_name = 'usage_logs'
-          AND column_name = 'cache_creation5m_tokens'
-    ) THEN
-        UPDATE usage_logs
-        SET cache_creation_5m_tokens = cache_creation5m_tokens
-        WHERE cache_creation_5m_tokens = 0
-          AND cache_creation5m_tokens <> 0;
-    END IF;
-
-    IF EXISTS (
-        SELECT 1
-        FROM information_schema.columns
-        WHERE table_schema = 'public'
-          AND table_name = 'usage_logs'
-          AND column_name = 'cache_creation1h_tokens'
-    ) THEN
-        UPDATE usage_logs
-        SET cache_creation_1h_tokens = cache_creation1h_tokens
-        WHERE cache_creation_1h_tokens = 0
-          AND cache_creation1h_tokens <> 0;
-    END IF;
-END $$;
+-- This migration drops the legacy columns to avoid confusion.
 
 ALTER TABLE usage_logs DROP COLUMN IF EXISTS cache_creation5m_tokens;
 ALTER TABLE usage_logs DROP COLUMN IF EXISTS cache_creation1h_tokens;