nuke: remove useless pages and REST API

[gaoxk]

Notion ticket link

NUKE IT LOL

Implementation description

• removed REST API
• removed all entity related models, mutations, queries, services
• removed default useless frontend pages and components

Steps to test

1. login
2. poke around
3. ???
4. profit

What should reviewers focus on?

• just make sure our app still works lmfao

Checklist

• My PR name is descriptive and in imperative tense
• My commit messages are descriptive and in imperative tense. My commits are atomic and trivial commits are squashed or fixup'd into non-trivial commits
• For backend changes, I have run the appropriate linters: docker exec -it <backend-container-id> /bin/bash -c "black . && isort --profile black ."
• I have requested a review from the PL, as well as other devs who have background knowledge on this PR or who will be building on top of this PR

[andrewyguo]

Nothing seemed to be broken 😎

Remember to pull the recent PR from main!

[gaoxk]

TFTR!