frontend: Fetch sponsorship based on queue numbers

[jo-elimu]

Fetch queue based on the current queueNumberFront and queueNumberNext.

The UI (Sponsorships.tsx) is currently broken because it incorrectly assumes that 1 is the queue number at the front of the queue, even after previous sponsorships have been processed and removed from the queue:

data: (3) [0n, 0n, '0x0000000000000000000000000000000000000000']