feat: migrate trade tools to write to actions table (new schema)

This commit implements Task 1 from the schema migration plan:
- Trade tools (buy/sell) now write to actions table instead of old positions table
- Added trading_day_id parameter to buy/sell functions
- Updated ContextInjector to inject trading_day_id
- Updated RuntimeConfigManager to include TRADING_DAY_ID in config
- Removed P&L calculation from trade functions (now done at trading_days level)
- Added tests verifying correct behavior with new schema

Changes:
- agent_tools/tool_trade.py: Modified _buy_impl and _sell_impl to write to actions table
- agent/context_injector.py: Added trading_day_id parameter and injection logic
- api/model_day_executor.py: Updated to read trading_day_id from runtime config
- api/runtime_manager.py: Added trading_day_id to config initialization
- tests/unit/test_trade_tools_new_schema.py: New tests for new schema compliance

All tests passing.

api/runtime_manager.py

@@ -48,7 +48,8 @@ class RuntimeConfigManager:
         self,
         job_id: str,
         model_sig: str,
-        date: str
+        date: str,
+        trading_day_id: int = None
     ) -> str:
         """
         Create isolated runtime config file for this execution.
@@ -57,6 +58,7 @@ class RuntimeConfigManager:
             job_id: Job UUID
             model_sig: Model signature
             date: Trading date (YYYY-MM-DD)
+            trading_day_id: Trading day record ID (optional, can be set later)
 
         Returns:
             Path to created runtime config file
@@ -79,7 +81,8 @@ class RuntimeConfigManager:
             "TODAY_DATE": date,
             "SIGNATURE": model_sig,
             "IF_TRADE": False,
-            "JOB_ID": job_id
+            "JOB_ID": job_id,
+            "TRADING_DAY_ID": trading_day_id
         }
 
         with open(config_path, "w", encoding="utf-8") as f: