Auto-compression still runs silently in the background with server-side
logging, but no longer sends messages to the user's chat about it.
Removed:
- 'Session is large... Auto-compressing' pre-compression notification
- 'Compressed: N → M messages' post-compression notification
- 'Session is still very large after compression' warning
- 'Auto-compression failed' warning
- Rate-limit tracking (only existed for these warnings)