feat: add pitrader_script step type + image vision for pipeline triggers

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>

pipelines/steps/__init__.py

@@ -7,6 +7,7 @@ from .claude_prompt import execute_claude_prompt
 from .template import execute_template
 from .api_call import execute_api_call
 from .skyvern import execute_skyvern
+from .pitrader_step import execute_pitrader
 
 logger = logging.getLogger(__name__)
 
@@ -16,6 +17,7 @@ STEP_EXECUTORS = {
     "template": execute_template,
     "api_call": execute_api_call,
     "skyvern": execute_skyvern,
+    "pitrader_script": execute_pitrader,
 }