iEduPortal Stage 6 — Login Fix 2

Fixes the remaining login issues:
- Staff class lookup uses store_result()/bind_result(), not get_result().
- One-time repair resets the three demo login passwords using password_hash().

Upload package contents to school-management-system/public/. Do NOT import SQL.

Repair URL:
https://ieduportal.com/school-management-system/public/upgrade/stage6resetall/?token=IEDU-STAGE6-RESET-3A8M7Q5K

Changes only:
admin ID 7 -> admin101 / admin101
parent ID 1 -> Parent1 / Parent1
staff ID 1 -> teacher1 / teacher1

Delete upgrade/stage6resetall/ immediately after successful repair.
