games/anki: Update to 26.09
- Migrate to Yarn v4 to be in sync with upstream. To ensure that the preinstalled Yarn v4 is actually used, a few minor workarounds and a new variable PREINSTALLED_YARN are required.
The latter is necessary because, with Yarn v2 and newer, environment variables prefixed with YARN_ can no longer be used.
- Sort pkg-plist while I'm here.
Changelog:
https://github.com/ankitects/anki/releases/tag/26.09
MFH: 2026Q3
Security: ce54d883-b060-11f1-b187-901b0edee044