Upgrade Typescript to 7 when ts-jest and NextJS properly support them

Upgrading to Typescript 7 causes (#43)

```bash
npm error code ERESOLVE
npm error ERESOLVE could not resolve
npm error
npm error While resolving: ts-jest@29.4.12
npm error Found: typescript@7.0.2
npm error node_modules/typescript
npm error typescript@"7.0.2" from the root project
npm error peerOptional typescript@">=3.3.1" from eslint-config-next@16.2.12
npm error node_modules/eslint-config-next
npm error dev eslint-config-next@"^16.2.12" from the root project
npm error 2 more (ts-api-utils, ts-node)
npm error
npm error Could not resolve dependency:
npm error peer typescript@">=4.3 <7" from ts-jest@29.4.12
npm error node_modules/ts-jest
npm error dev ts-jest@"^29.4.12" from the root project
npm error
npm error Conflicting peer dependency: typescript@6.0.3
npm error node_modules/typescript
npm error peer typescript@">=4.3 <7" from ts-jest@29.4.12
npm error node_modules/ts-jest
npm error dev ts-jest@"^29.4.12" from the root project
npm error
npm error Fix the upstream dependency conflict, or retry this command with --force or --legacy-peer-deps to accept an incorrect (and potentially broken) dependency resolution.
```

`ts-jest` has a workaround: https://kulshekhar.github.io/ts-jest/docs/next/guides/typescript-7 but this then causes a problem with NextJS as discussed in https://github.com/vercel/next.js/discussions/95633. The fix suggested does not work.

Start by reproducing the npm dependency-resolution error, then read the linked ts-jest TypeScript 7 workaround and the referenced Next.js discussion. Done means TypeScript 7, ts-jest, and Next.js can be installed together without an unsupported workaround and the site’s existing checks still pass.

Written by the indexing model from the issue text.