fix: resolve async execution and position storage issues

- Fix async call in model_day_executor.py by wrapping with asyncio.run()
  Resolves RuntimeWarning where run_trading_session coroutine was never awaited
- Remove register_agent() call in API mode to prevent file-based position storage
  Position data is now stored exclusively in SQLite database (jobs.db)
- Update test mocks to use AsyncMock for async run_trading_session method

This fixes production deployment issues:
1. Trading sessions now execute properly (async bug)
2. No position files created, database-only storage
3. All tests pass

Closes issue with no trades being executed in production

tests/unit/test_model_day_executor.py

@@ -14,7 +14,7 @@ Tests verify:
 
 import pytest
 import json
-from unittest.mock import Mock, patch, MagicMock
+from unittest.mock import Mock, patch, MagicMock, AsyncMock
 from pathlib import Path
 
 
@@ -29,7 +29,8 @@ def create_mock_agent(positions=None, last_trade=None, current_prices=None,
     mock_agent.get_current_prices.return_value = current_prices or {}
     mock_agent.get_reasoning_steps.return_value = reasoning_steps or []
     mock_agent.get_tool_usage.return_value = tool_usage or {}
-    mock_agent.run_trading_session.return_value = session_result or {"success": True}
+    # run_trading_session is async, so use AsyncMock
+    mock_agent.run_trading_session = AsyncMock(return_value=session_result or {"success": True})
 
     return mock_agent