Add Batch Background Check Export and Import

Issue Description

CELTS would like the ability to manage student background checks in batches instead of updating each student individually from their user profile.

Under the current Reports section, which could be renamed to Data Management or Download and Upload, add a feature that allows CELTS Admins to download a spreadsheet containing students who may require background check tracking. This should include students who:

Are interested volunteers, Have previously volunteered, Are Bonners, Are CELTS Student Staff, Are members of the Operations Team

Each row in the spreadsheet should represent one student. The spreadsheet should contain columns for the different background check records and the dates associated with those background checks.

Background check statuses should support:

Not Submitted, Submitted, Passed, Failed

If a student does not currently have a background check status, the spreadsheet should default that record to Not Submitted.

To make batch editing easier and reduce invalid data, background check status cells should use a dropdown containing the allowed statuses. Background check date fields should also use date-formatted/validated cells so users can select or enter valid dates instead of entering unrestricted text both are available in openpyxl which is part of our standard code in CELTS.

After CELTS staff make their changes, they should be able to upload the spreadsheet back into CELTS. The system should parse the uploaded file, validate the data, match each row to the appropriate student, and update the corresponding background check records.

Start by locating the existing Reports section and the student background-check records, then review how Python and openpyxl are currently used for spreadsheet operations. Done means CELTS Admins can export the specified students and records, edit validated statuses and dates, and upload a file that validates, matches students, and updates their background checks.

Written by the indexing model from the issue text.