Removed unused imports and variables

[thomasvaeth]

Summary

• Enabled noUnusedLocals in tsconfig.json and removed all unused imports and variables
  • Opted for noUnusedLocals over adding ESLint to keep the toolchain light
  • I did not enable noUnusedParameters, but there were another 28 errors there if following up
• Fixed optional chaining consistency for children snippet
• Ran Prettier across the codebase

Test plan

• Run npm run check to confirm no TypeScript errors
• Smoke test the status page, admin dashboard, and embed routes