fix: resolve critical integration issues in BaseAgent P&L calculation

Critical fixes:
1. Fixed api/database.py import - use get_db_path() instead of non-existent get_database_path()
2. Fixed state management - use database queries instead of reading from position.jsonl file
3. Fixed action counting - track during trading loop execution instead of retroactively from conversation history
4. Completed integration test to verify P&L calculation works correctly

Changes:
- agent/base_agent/base_agent.py:
  * Updated _get_current_portfolio_state() to query database via get_current_position_from_db()
  * Added today_date and job_id parameters to method signature
  * Count trade actions during trading loop instead of post-processing conversation history
  * Removed obsolete action counting logic

- api/database.py:
  * Fixed import to use get_db_path() from deployment_config
  * Pass correct default database path "data/trading.db"

- tests/integration/test_agent_pnl_integration.py:
  * Added proper mocks for dev mode and MCP client
  * Mocked get_current_position_from_db to return test data
  * Added comprehensive assertions to verify trading_day record fields
  * Test now actually validates P&L calculation integration

Test results:
- All unit tests passing (252 passed)
- All P&L integration tests passing (8 passed)
- No regressions detected

api/database.py

@@ -553,8 +553,8 @@ class Database:
                      If None, uses default from deployment config.
         """
         if db_path is None:
-            from tools.deployment_config import get_database_path
-            db_path = get_database_path()
+            from tools.deployment_config import get_db_path
+            db_path = get_db_path("data/trading.db")
 
         self.db_path = db_path
         self.connection = sqlite3.connect(db_path, check_same_thread=False)