Kl/scrum 56 email notifications

[kevin-lann]

Description

SCRUM-56

This PR Includes:

• Email Notifications for upcoming course events
  • Ran every 1 min by server
  • If an event is starting within the next 15 min then notify the user to which that event belongs to by email
• User is able to toggle notifications on and off for individual timetables using the kebab menu
• Unit tests for email notifications

Screenshots

HOW TO TEST
Update env varirables in backend (in pinned msg on discod)
Since all of our course events are in the future (Summer 2025 at earliest) we have to mock the current date to test.
Go to /backend/constants/constants.ts and modify these variables:

// true - notifications will be tested by mocking current Date
// false - normal application behavior
export const TEST_NOTIFICATIONS = false;
// Mock the current date
// Note: month index in date constructor is 0 indexed (0 - 11)
export const TEST_DATE_NOW = new Date(2025, 4, 14, 8, 45, 1);

In this example, we are pretending the current date is Wed May 14th, 2025 at 8:45:01 am
Note that month index is 0 indexed (0-11)

Type of change

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

Checklist:

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings

[thomasyzy7]

Cancel button doesn't work.

Also I got 13 emails at the same time when doing notifications

[thomasyzy7]

Now, we need to prevent the same email from sending multiple times.