Add pitrader_script executor for running PITrader scripts (pi-scan,
playbook, execute_trades) as pipeline steps with vault credential
injection and JSON output capture.
Extend claude_prompt step with vision support (image_b64 in trigger
context). Add image pipeline trigger to on_image_message handler.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
