[imorland]

Changes proposed in this pull request:
Brings the JS tooling in line with flarum/framework and @flarum/cli:

• flarum-webpack-config: ^3.0.0 → ^3.1.0
• typescript: added at ^5.9.3
• webpack-cli: ^4.9.1 → ^7.2.3

typescript is declared directly so tsc stays linked under package managers that only link the binaries of direct dependencies. webpack-cli 7 needs Node 20.9 or later. yarn.lock is updated without a full regeneration.

No release needed: the rebuilt bundle is not expected to change.

Reviewers should focus on:
No source changes. yarn format-check and yarn build pass (there is no check-typings script). regenerate is deduplicated to 1.5.0, as jest-config's README recommends, so Babel does not end up with two copies.

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.