fix(chat_completions): strip tool_name from messages for strict providers

The 'tool_name' key on role=tool messages is an internal Hermes field
(stored in the messages.tool_name SQLite column for FTS indexing) that
is not part of the OpenAI Chat Completions schema. Strict OpenAI-compatible
providers — notably Moonshot AI (Kimi) — reject it with HTTP 400:

  Error from provider: Extra inputs are not permitted,
  field: 'messages[N].tool_name', value: 'execute_code'

Add 'tool_name' to the sanitize block in ChatCompletionsTransport.convert_messages
alongside the existing Codex Responses API fields (codex_reasoning_items,
codex_message_items) so it is popped before the request is sent.

Reproducer:
  hermes chat --model kimi-k2.6
  > list the top 5 Hacker News stories
  -> assistant emits tool_call(execute_code)
  -> tool result message gets tool_name='execute_code'
  -> next turn's payload includes messages[N].tool_name -> 400

Permissive backends (MiniMax, OpenRouter on most routes) ignore the extra
field and were masking the bug.

agent/transports/chat_completions.py

@@ -122,7 +122,11 @@ class ChatCompletionsTransport(ProviderTransport):
         for msg in messages:
             if not isinstance(msg, dict):
                 continue
-            if "codex_reasoning_items" in msg or "codex_message_items" in msg:
+            if (
+                "codex_reasoning_items" in msg
+                or "codex_message_items" in msg
+                or "tool_name" in msg
+            ):
                 needs_sanitize = True
                 break
             tool_calls = msg.get("tool_calls")
@@ -145,6 +149,7 @@ class ChatCompletionsTransport(ProviderTransport):
                 continue
             msg.pop("codex_reasoning_items", None)
             msg.pop("codex_message_items", None)
+            msg.pop("tool_name", None)
             tool_calls = msg.get("tool_calls")
             if isinstance(tool_calls, list):
                 for tc in tool_calls: