feat(ft546): persist shadow comparison evidence

ruoyi-wcs-shadow/src/main/java/com/ruoyi/shadow/kernel/ShadowCycleResult.java

@@ -47,6 +47,12 @@ public final class ShadowCycleResult {
                 encodedCommands);
     }
 
+    public static ShadowCycleResult degraded(String reasonCode) {
+        return new ShadowCycleResult("DEGRADED", reasonCode, null,
+                Collections.<Ft546SrgvCommandIntent>emptyList(),
+                Collections.<Ft546EncodedCommand>emptyList());
+    }
+
     public String getStatusCode() { return statusCode; }
     public String getReasonCode() { return reasonCode; }
     public DispatchCycleResult getDecisions() { return decisions; }