feat: add global system notices and Beijing order time display

internal/store/portal_notice_test.go

@@ -0,0 +1,13 @@
+package store
+
+import (
+	"testing"
+	"time"
+)
+
+func TestFormatNoticeBusinessTimeUsesShanghaiWallClock(t *testing.T) {
+	value := time.Date(2026, 10, 22, 6, 12, 38, 0, time.UTC)
+	if got, want := formatNoticeBusinessTime(value), "2026-10-22 14:12:38"; got != want {
+		t.Fatalf("formatNoticeBusinessTime() = %q, want %q", got, want)
+	}
+}