feat(channels): add send_progress option to control progress message delivery

Add a boolean config option `channels.sendProgress` (default: false) to
control whether progress messages (marked with `_progress` metadata) are
sent to chat channels. When disabled, progress messages are filtered
out in the outbound dispatcher.

nanobot/channels/manager.py

@@ -193,6 +193,9 @@ class ChannelManager:
                     timeout=1.0
                 )
                 
+                if msg.metadata.get("_progress") and not self.config.channels.send_progress:
+                    continue
+                
                 channel = self.channels.get(msg.channel)
                 if channel:
                     try: