* refactor: migrate i18n files from YAML to TOML format and simplify structure
* refactor: make translation file adjust to gohugoio/locales language code so date translation can work properly
* refactor: use hyphens instead of underscores for i18n, because that's how Hugo pick the translation file
* docs: update comments for i18n language availability and CJK language detection in hugo.toml.
* refactor: remove jsconfig.json
* chore: remove devcontainer config
* refactor: migrate Hugo configuration from `hugo.yaml` to dedicated `module.toml` and `params.toml` files, and update minimum Hugo version.
* refactor: migrate demo site configuration from `hugo.yaml` to `config/_default/*.toml`
* feat: enable local sidebar avatar for demo site and relocate its image to demo assets.
* feat: migrate demo site to Hugo Modules for theme management.
* fix: wrong config folder name
