Rename the ADP Yii 3 framework adapter from "Yiisoft" to "Yii3" for clarity
and consistency — "Yiisoft" is the framework organization name, "Yii3" is the
framework version our adapter targets.

Changes across ~200 files:
- Directory: libs/Adapter/Yiisoft → libs/Adapter/Yii3
- Playground: playground/yiisoft-app → playground/yii3-app
- PHP namespace: AppDevPanel\Adapter\Yiisoft → AppDevPanel\Adapter\Yii3
- Composer package: app-dev-panel/adapter-yiisoft → app-dev-panel/adapter-yii3
- Config key: app-dev-panel/yiisoft → app-dev-panel/yii3
- Makefile targets/variables: *-yiisoft → *-yii3, YIISOFT_PORT → YII3_PORT
- CI workflows, split repos, build scripts
- All documentation (EN + RU), CLAUDE.md files, README, CONTRIBUTING
- IDE configs (.idea/, .iml)
- Website: guide pages, class registry, VitePress config

Yiisoft framework references (yiisoft/* packages, Yiisoft\ namespaces) preserved.

https://claude.ai/code/session_01SrLZYFtnK8Hy6U2oPDBi4B