fix(harness): allow MemoryFlushMiddleware to flush for all Agent types

MemoryFlushMiddleware.doFlush() checked `instanceof ReActAgent` before
flushing memories, which silently skipped HarnessAgent (it implements
Agent directly, not via ReActAgent). This caused daily memory journals
(MEMORY type) and consolidated MEMORY.md (CONTEXT type) to never be
written for HarnessAgent-based agents.

Remove the ReActAgent type guard since RuntimeContext.resolveAgentState()
accepts any Agent, and HarnessAgent provides getAgentState() via its
delegate.

Closes #2030

Author: chickenlj

agentscope-harness/src/main/java/io/agentscope/harness/agent/middleware/MemoryFlushMiddleware.java

@@ -15,7 +15,6 @@
  */
 package io.agentscope.harness.agent.middleware;
 
-import io.agentscope.core.ReActAgent;
 import io.agentscope.core.agent.Agent;
 import io.agentscope.core.agent.RuntimeContext;
 import io.agentscope.core.event.AgentEvent;
@@ -156,10 +155,7 @@ public Flux<AgentEvent> onAgent(
     }
 
     private Mono<Void> doFlush(Agent agent, RuntimeContext rc) {
-        if (!(agent instanceof ReActAgent reActAgent)) {
-            return Mono.empty();
-        }
-        AgentState state = RuntimeContext.resolveAgentState(rc, reActAgent);
+        AgentState state = RuntimeContext.resolveAgentState(rc, agent);
         if (state == null) {
             return Mono.empty();
         }
@@ -216,7 +212,7 @@ private Mono<Void> doFlush(Agent agent, RuntimeContext rc) {
      * namespace (see {@link #timerKeyFor(RuntimeContext)}).
      *
      * <p>Package-private for unit testing of the trigger gate without standing up a full
-     * {@code ReActAgent}.
+     * {@code Agent}.
      */
     boolean shouldFlushNow(RuntimeContext rc) {
         switch (flushTrigger.mode()) {