fix(logger): 修复 caller 字段与 OpsSystemLogSink 停止刷盘

修复点：

- zap logger 不再强制 AddCallerSkip(1)，确保 caller 指向真实调用点

- slog handler 避免重复写 time 字段

- OpsSystemLogSink 优先从字段 component 识别业务组件；停止时 drain 队列并用可用 ctx 刷盘

补充：新增/完善对应单测

backend/internal/service/ops_system_log_sink_test.go

@@ -36,11 +36,29 @@ func TestOpsSystemLogSink_ShouldIndex(t *testing.T) {
 			event: &logger.LogEvent{Level: "info", Component: "http.access"},
 			want:  true,
 		},
+		{
+			name: "access component from fields (real zap path)",
+			event: &logger.LogEvent{
+				Level:     "info",
+				Component: "",
+				Fields:    map[string]any{"component": "http.access"},
+			},
+			want: true,
+		},
 		{
 			name:  "audit component",
 			event: &logger.LogEvent{Level: "info", Component: "audit.log_config_change"},
 			want:  true,
 		},
+		{
+			name: "audit component from fields (real zap path)",
+			event: &logger.LogEvent{
+				Level:     "info",
+				Component: "",
+				Fields:    map[string]any{"component": "audit.log_config_change"},
+			},
+			want: true,
+		},
 		{
 			name:  "plain info",
 			event: &logger.LogEvent{Level: "info", Component: "app"},
@@ -205,6 +223,47 @@ func TestOpsSystemLogSink_FlushFailureUpdatesHealth(t *testing.T) {
 	t.Fatalf("write_failed_count not updated")
 }
 
+func TestOpsSystemLogSink_StopFlushUsesActiveContextAndDrainsQueue(t *testing.T) {
+	var inserted int64
+	var canceledCtxCalls int64
+	repo := &opsRepoMock{
+		BatchInsertSystemLogsFn: func(ctx context.Context, inputs []*OpsInsertSystemLogInput) (int64, error) {
+			if err := ctx.Err(); err != nil {
+				atomic.AddInt64(&canceledCtxCalls, 1)
+				return 0, err
+			}
+			atomic.AddInt64(&inserted, int64(len(inputs)))
+			return int64(len(inputs)), nil
+		},
+	}
+
+	sink := NewOpsSystemLogSink(repo)
+	sink.batchSize = 200
+	sink.flushInterval = time.Hour
+	sink.Start()
+
+	sink.WriteLogEvent(&logger.LogEvent{
+		Time:      time.Now().UTC(),
+		Level:     "warn",
+		Component: "app",
+		Message:   "pending-on-shutdown",
+		Fields:    map[string]any{"component": "http.access"},
+	})
+
+	sink.Stop()
+
+	if got := atomic.LoadInt64(&inserted); got != 1 {
+		t.Fatalf("inserted = %d, want 1", got)
+	}
+	if got := atomic.LoadInt64(&canceledCtxCalls); got != 0 {
+		t.Fatalf("canceled ctx calls = %d, want 0", got)
+	}
+	health := sink.Health()
+	if health.WrittenCount != 1 {
+		t.Fatalf("written_count = %d, want 1", health.WrittenCount)
+	}
+}
+
 type stringerValue string
 
 func (s stringerValue) String() string { return string(s) }