[imorland]

Changes proposed in this pull request:
Follow-up to #85, matching the tooling flarum/framework and @flarum/cli now use.

• Declares typescript: ^5.9.3. [2.x] chore: bump @flarum/jest-config to ^2.1.1 and drop the typescript devDependency #85 removed the old ^4.5.4 so TypeScript came from flarum-webpack-config, but a direct declaration keeps tsc linked under package managers that only link the binaries of direct dependencies (pnpm, Yarn 4). tsc stays at 5.9.3.
• Bumps webpack-cli from ^4.9.1 to ^7.2.3. It needs Node 20.9 or later.

yarn.lock is updated without a full regeneration.

Reviewers should focus on:
No source changes, so no release is needed. yarn check-typings, yarn format-check and yarn build pass.

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Frontend changes: tests are green (run yarn test in js/).
• Frontend changes: tests have been added, or are not appropriate here.
• Core developer confirmed locally this works as intended.
• The description above is written by me and describes what this pull request actually does.