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

agent/conversation_loop.py

@@ -474,6 +474,7 @@ def run_conversation(
     task_id: str = None,
     stream_callback: Optional[callable] = None,
     persist_user_message: Optional[str] = None,
+    persist_user_timestamp: Optional[float] = None,
 ) -> Dict[str, Any]:
     """
     Run a complete conversation with tool calling until completion.
@@ -489,6 +490,8 @@ def run_conversation(
         persist_user_message: Optional clean user message to store in
             transcripts/history when user_message contains API-only
             synthetic prefixes.
+        persist_user_timestamp: Optional platform event timestamp to store
+            as metadata on that persisted user message.
                 or queuing follow-up prefetch work.
 
     Returns:
@@ -510,6 +513,7 @@ def run_conversation(
         task_id,
         stream_callback,
         persist_user_message,
+        persist_user_timestamp,
         restore_or_build_system_prompt=_restore_or_build_system_prompt,
         install_safe_stdio=_install_safe_stdio,
         sanitize_surrogates=_sanitize_surrogates,