process_live.py fails if processed/trades.csv does not exist

[dafalcon]

Steps to reproduce:

rm -f processed/trades.csv
uv run python update_all.py

# ... 

Processing live
============================================================
🔄 Processing Live Trades
============================================================
⚠ No existing processed file found - processing from beginning

📂 Reading: goldsky/orderFilled.csv
✓ Loaded 13,004 rows
Traceback (most recent call last):
  File "/Users/dafalcon/projects/poly_data/update_all.py", line 11, in <module>
    process_live()
  File "/Users/dafalcon/projects/poly_data/update_utils/process_live.py", line 145, in process_live
    same_timestamp = df.filter(pl.col('timestamp') == last_processed['timestamp'])
KeyError: 'timestamp'