fix: update StaticLongTermMemoryHookTest to expect memory at index 0

The test was asserting memory message at index 1 (end), which matched
the old buggy behavior. Update to assert index 0 (beginning) to align
with the fix in #1164.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Fruank4

agentscope-core/src/test/java/io/agentscope/core/memory/StaticLongTermMemoryHookTest.java

@@ -138,13 +138,13 @@ void testOnEventWithPreReasoningEventAndRetrievedMemories() {
                         resultEvent -> {
                             List<Msg> messages = resultEvent.getInputMessages();
                             assertEquals(2, messages.size());
-                            assertEquals(MsgRole.SYSTEM, messages.get(1).getRole());
+                            assertEquals(MsgRole.SYSTEM, messages.get(0).getRole());
                             assertTrue(
-                                    messages.get(1)
+                                    messages.get(0)
                                             .getTextContent()
                                             .contains("<long_term_memory>"));
                             assertTrue(
-                                    messages.get(1)
+                                    messages.get(0)
                                             .getTextContent()
                                             .contains("User prefers dark mode"));
                         })