feat(sse): sync H-104 contract

Author: loong10k

src/main/java/io/github/easy4j/hermes/api/sse/SseContinuityStatus.java

@@ -0,0 +1,15 @@
+package io.github.easy4j.hermes.api.sse;
+
+/**
+ * Describes whether event continuity across the current observation has been proven.
+ *
+ * @since 1.0.0
+ */
+public enum SseContinuityStatus {
+    /** The subscription is still on its original transport connection. */
+    INITIAL,
+    /** The subscription reattached without a verified replay cursor or equivalent proof. */
+    UNVERIFIED,
+    /** The server contract explicitly proved replay continuity. */
+    VERIFIED
+}