build-a-bear backend implementation

[jjasonguo]

Summary

This is the backend of the build a bear feature

• created Schema, DTO, Service, Gateway, Module based on existing patterns / design in the app
• made preliminary e2e tests (in the works, will add more/modify along with more specific user interactions when i develop frontend next sem
• NOTE: prisma migration has a lot more than my PR because of prisma version update (Temi and I think)

SCHEMA CHANGES

Remaining TODOs:

• implement frontend

Test Plan

E2E TESTS INCLUDED

[dti-github-bot]

[diff-counting] Significant lines: 798.

[jiminkim214]

Great Work Jason! I noticed that in avatar.dto, the RequestUserInventoryDto and RequestUserBearLoadoutDto are empty. Remove them if unnecessary, or add a comment explaining their purpose. Other than that, everything looks awesome!

[3TTemi]

Backend changes look good, good job on this PR.

But we should check out this one possible race condition in avatar service.
Line 109: if (balance < item.cost) checks the value in memory. Line 117: score: { decrement: item.cost } updates the DB.

The system checks the user's balance, and then separately deducts the cost. If a user clicks "Buy" very quickly twice, both clicks can pass the initial check and deduct the cost twice, resulting in a negative balance.