Set defaults for date/time picker and timezone

[asarj]

Summary

Fixes #1884

The due date picker in the formgrader's "Manage Assignments" page had two UX issues: the time component defaulted to the current time instead of midnight, and the timezone field was empty in the create modal. Faculty would unintentionally save inconsistent due times like 14:37 when they only changed the date.

Changes

• Pass the server's configured timezone offset to the template and pre-fill it in the create modal
• On first click into an empty date field, default to today at 00:00 (using a one-time focus handler so users who skip the field get no due date)
• Existing due dates in the edit modal are preserved unchanged

Tests

• Backend: test_get_assignment_custom_timezone: verifies non-UTC timezone propagation
• E2E: Due date defaults: validates midnight default on focus, timezone pre-fill, and no-date regression

Manual verification

1. "Add new assignment..." --> timezone pre-filled, date empty
2. Click into date field --> defaults to today at 00:00
3. Save without touching date --> due date is "None"
4. Edit existing assignment --> original date/time preserved

Per the pull request guidelines:

• Added regression tests
• No documentation changes needed

[github-actions]

👈 Launch a Binder on branch asarj/nbgrader/add-defaults-for-due-date-time-picker

[asarj]

Manual Steps to test after launching a JupyterLab instance

1. Press Ctrl/Cmd + Shift + C, type "formgrader", click "Formgrader"
2. You should be redirected to the "Manage Assignments" page
3. Verify there is a "hw1" entry already populated

Test the create modal:

4. Click "Add new assignment..." at the bottom
5. Check: timezone field should show +0000 (not empty)
6. Check: date field should be empty
7. Click into the date field
8. Check: it should fill with today's date at 00:00
9. Click Cancel

Test saving without a date:

10. Click "Add new assignment..." again
11. Type test1 in the Name field
12. Do NOT touch the date field
13. Click Save
14. Check: the assignment should show due date as "None"

Test saving with a date:

15. Click "Add new assignment..." again
16. Type test2 in the Name field
17. Click into the date field (it fills with today at 00:00)
18. Change the date to tomorrow, leave time at 00:00
19. Click Save
20. Check: the assignment should show tomorrow's date with time 00:00:00

Test the edit modal:

21. Click the pencil icon next to test2
22. Check: the existing date/time should be preserved (not overwritten)
23. Click Cancel
24. Click the pencil icon next to test1 (no due date)
25. Check: date field is empty
26. Click into the date field
27. Check: it fills with today at 00:00

[asarj]

hi @brichet can you please trigger the CI checks again?

[asarj]

Seems the lone failing test was due to 20 min timeout, is it permissible to increase the timeout to something longer (like 30 mins) or somehow increase the number of workers that execute CI tests?