fix: update position queries to use new trading_days schema

Changes:
- Update get_today_init_position_from_db to query trading_days table
- Remove obsolete add_no_trade_record_to_db calls from BaseAgent
- Simplify _handle_trading_result (trading_day record handles both scenarios)

Root Cause:
- Code was still querying old positions table after schema migration
- The add_no_trade_record_to_db function is obsolete in new schema

New Schema Behavior:
- trading_day record created at session start (regardless of trading)
- trading_day record updated at session end with final results
- No separate "no-trade" record needed

Impact:
- Fixes: "no such table: positions" error in get_today_init_position_from_db
- Removes unnecessary database writes for no-trade scenarios
- Simplifies codebase by removing obsolete function calls

Related: tools/price_tools.py:340-364, agent/base_agent/base_agent.py:661-673

tools/price_tools.py

@@ -337,12 +337,12 @@ def get_today_init_position_from_db(
     cursor = conn.cursor()
 
     try:
-        # Get most recent position before today
+        # Get most recent trading day before today
         cursor.execute("""
-            SELECT p.id, p.cash
-            FROM positions p
-            WHERE p.job_id = ? AND p.model = ? AND p.date < ?
-            ORDER BY p.date DESC, p.action_id DESC
+            SELECT id, ending_cash
+            FROM trading_days
+            WHERE job_id = ? AND model = ? AND date < ?
+            ORDER BY date DESC
             LIMIT 1
         """, (job_id, modelname, today_date))
 
@@ -353,15 +353,15 @@ def get_today_init_position_from_db(
             logger.info(f"No previous position found for {modelname}, returning initial cash")
             return {"CASH": 10000.0}
 
-        position_id, cash = row
+        trading_day_id, cash = row
         position_dict = {"CASH": cash}
 
-        # Get holdings for this position
+        # Get holdings for this trading day
         cursor.execute("""
             SELECT symbol, quantity
             FROM holdings
-            WHERE position_id = ?
-        """, (position_id,))
+            WHERE trading_day_id = ?
+        """, (trading_day_id,))
 
         for symbol, quantity in cursor.fetchall():
             position_dict[symbol] = quantity