Remove job_id filter from get_previous_trading_day() SQL query to enable
portfolio continuity across jobs. Previously, new jobs would reset to
initial $10,000 cash instead of continuing from previous job's ending
position.
Root cause: get_previous_trading_day() filtered by job_id, while
get_current_position_from_db() correctly queries across all jobs.
This inconsistency caused starting_cash to default to initial_cash
when no previous day was found within the same job.
Changes:
- api/database.py: Remove job_id filter from SQL WHERE clause
- tests/unit/test_database_helpers.py: Add test for cross-job continuity
Fixes position tracking bug where subsequent jobs on consecutive dates
would not recognize previous day's holdings from different job.