Feature/Grant Extension Modal For Admins

[JoeMacl]

Description

This PR implements the Staff Grant Extension form as a modal dialog for admins. The feature allows staff to select a student, specify an extension duration, and provide a reason from an angular material based popup form. This feature is accessible for admins under the units page.

Note: This branch only contains frontend related changes.

Full documentation for this feature can be found here: https://thoth-tech.netlify.app/products/ontrack/projects/staff-grant-extension/design/

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• Manually tested the modal form in the browser using different inputs
• Verified that selected student, duration, and reason values are correctly logged/submitted
• Confirmed success and error messages appear appropriately
• Checked responsive layout across screen sizes
• Validated that the form resets correctly after submission
• Confirmed admin access via the Units page (where the "Request Extension" button is usually found)

Screenshots

Testing Checklist:

• Tested in latest Chrome
• Tested in latest Safari
• Tested in latest Firefox

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings