feat(gateway): inject stable human-readable message timestamps

Consolidates these related Amy fork patches:
- 429830f39 feat(gateway): inject message timestamps into user messages for LLM context
- 3c3d6fac0 fix: handle both ISO string and epoch float timestamps in history replay
- 2874f7725 feat: human-friendly timestamp format with weekday and timezone name
- 3735f4c8b fix: render gateway message timestamps once

tests/gateway/test_fast_command.py

@@ -23,12 +23,20 @@ class _CapturingAgent:
         type(self).last_init = dict(kwargs)
         self.tools = []
 
-    def run_conversation(self, user_message, conversation_history=None, task_id=None, persist_user_message=None):
+    def run_conversation(
+        self,
+        user_message,
+        conversation_history=None,
+        task_id=None,
+        persist_user_message=None,
+        persist_user_timestamp=None,
+    ):
         type(self).last_run = {
             "user_message": user_message,
             "conversation_history": conversation_history,
             "task_id": task_id,
             "persist_user_message": persist_user_message,
+            "persist_user_timestamp": persist_user_timestamp,
         }
         return {
             "final_response": "ok",