fix(zulip): use PATCH /api/v1/messages/{id} for message editing

Zulip API edits messages via PATCH /api/v1/messages/{message_id}
(POST returns 405 on this endpoint). Also:
- edit_message() now returns SendResult (not bool) for Gateway compatibility
- Clean up duplicate gateway instances before restart

plugins/platforms/zulip/adapter.py

@@ -910,10 +910,11 @@ class ZulipAdapter(BasePlatformAdapter):
         # Send actual content
         result = await self._send_api_call(payload)
         if result and result.get("id"):
+            msg_id = str(result["id"])
             self._health_stats["send_count"] += 1
             return SendResult(
                 success=True,
-                message_id=str(result["id"]),
+                message_id=msg_id,
             )
 
         self._health_stats["send_errors"] += 1
@@ -942,8 +943,9 @@ class ZulipAdapter(BasePlatformAdapter):
             "content": truncated,
         }
         try:
+            # Zulip API: PATCH /api/v1/messages/{message_id} with content in body
             resp, status = await self._api_call(
-                "POST", f"/api/v1/messages/{int(message_id)}",
+                "PATCH", f"/api/v1/messages/{int(message_id)}",
                 data=payload,
             )
             if resp: