Fix timesheet double-counting bug; add Holiday row to general section

- autosave.php: subtract job-synced hours before saving manual entries
  to prevent duplication when returning to timesheet after editing a job
- timesheet_edit.php: remove PTO category sub-header row, add Holiday
  account (HOL), hide code column for general section rows

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
