fix(slack): skip thread context for slash commands so /restart is not buried

_with_thread_context prepends conversation history to the message
content.  This turned "/restart" into "Slack thread context...\n\n
Current message:\n/restart", which the command router could not match
as a priority command.  Skip the context enrichment when the stripped
text starts with "/".

Made-with: Cursor

nanobot/channels/slack.py

@@ -348,7 +348,8 @@ class SlackChannel(BaseChannel):
 
         # Thread-scoped session key for channel/group messages
         session_key = f"slack:{chat_id}:{thread_ts}" if thread_ts and channel_type != "im" else None
-        content = await self._with_thread_context(
+        is_slash = text.strip().startswith("/")
+        content = text if is_slash else await self._with_thread_context(
             text,
             chat_id=chat_id,
             channel_type=channel_type,