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/pkg/logger/slog_handler_test.go

@@ -0,0 +1,90 @@
+package logger
+
+import (
+	"context"
+	"log/slog"
+	"testing"
+	"time"
+
+	"go.uber.org/zap"
+	"go.uber.org/zap/zapcore"
+)
+
+type captureState struct {
+	writes []capturedWrite
+}
+
+type capturedWrite struct {
+	entry  zapcore.Entry
+	fields []zapcore.Field
+}
+
+type captureCore struct {
+	state      *captureState
+	withFields []zapcore.Field
+}
+
+func newCaptureCore() *captureCore {
+	return &captureCore{state: &captureState{}}
+}
+
+func (c *captureCore) Enabled(zapcore.Level) bool {
+	return true
+}
+
+func (c *captureCore) With(fields []zapcore.Field) zapcore.Core {
+	nextFields := make([]zapcore.Field, 0, len(c.withFields)+len(fields))
+	nextFields = append(nextFields, c.withFields...)
+	nextFields = append(nextFields, fields...)
+	return &captureCore{
+		state:      c.state,
+		withFields: nextFields,
+	}
+}
+
+func (c *captureCore) Check(entry zapcore.Entry, ce *zapcore.CheckedEntry) *zapcore.CheckedEntry {
+	return ce.AddCore(entry, c)
+}
+
+func (c *captureCore) Write(entry zapcore.Entry, fields []zapcore.Field) error {
+	allFields := make([]zapcore.Field, 0, len(c.withFields)+len(fields))
+	allFields = append(allFields, c.withFields...)
+	allFields = append(allFields, fields...)
+	c.state.writes = append(c.state.writes, capturedWrite{
+		entry:  entry,
+		fields: allFields,
+	})
+	return nil
+}
+
+func (c *captureCore) Sync() error {
+	return nil
+}
+
+func TestSlogZapHandler_Handle_DoesNotAppendTimeField(t *testing.T) {
+	core := newCaptureCore()
+	handler := newSlogZapHandler(zap.New(core))
+
+	record := slog.NewRecord(time.Date(2026, 1, 1, 12, 0, 0, 0, time.UTC), slog.LevelInfo, "hello", 0)
+	record.AddAttrs(slog.String("component", "http.access"))
+
+	if err := handler.Handle(context.Background(), record); err != nil {
+		t.Fatalf("handle slog record: %v", err)
+	}
+	if len(core.state.writes) != 1 {
+		t.Fatalf("write calls = %d, want 1", len(core.state.writes))
+	}
+
+	var hasComponent bool
+	for _, field := range core.state.writes[0].fields {
+		if field.Key == "time" {
+			t.Fatalf("unexpected duplicate time field in slog adapter output")
+		}
+		if field.Key == "component" {
+			hasComponent = true
+		}
+	}
+	if !hasComponent {
+		t.Fatalf("component field should be preserved")
+	}
+}