The /admin/time-tracking overview page crashed on render with
`column "fw.display_name" does not exist`. Cycle 10 unified
`time_tracking_workers` + `water_irrigators` into `field_workers`,
which uses `name` and `pin_hash` (not the legacy `display_name` /
`pin` from `admin_users`). This fix aligns the SQL, row type, and
result mapper with the actual schema.
End-to-end verified against water.tuxedocorn.com with worker PIN 2229:
PIN auth, task picker, clock-in, and clock-out all succeed with no
console errors and no failed HTTP requests.
Includes a regression test that fails on the buggy SQL (4/8 fail) and
passes after the fix (8/8 pass). Covers the column contract, row
projection, empty-result + unauthenticated boundaries, and null
aggregate coercion.
Nora