fix: add .prettierrc and fix code formatting

[huyenltnguyen]

Checklist:

• I have read freeCodeCamp's contribution guidelines.
• My pull request has a descriptive title (not a vague title like Update index.md)

CI was failing with Prettier formatting errors (#6) because:

• Locally, Prettier was inheriting configuration from the parent repo (https://github.com/freeCodeCamp/freeCodeCamp/blob/main/.prettierrc)
  • I checked this by running pnpm prettier --find-config-path apps/api/configs/super-block-list.ts
• In CI, the challenge-editor runs standalone (not as a submodule), so Prettier used default settings
• This mismatch caused formatting differences between local and CI environments