fix: move from devenv to nix flake

...manual/de/book/fonts/open-sans-v17-all-charsets-800.woff2

.../de/book/fonts/open-sans-v17-all-charsets-800italic.woff2

...ual/de/book/fonts/open-sans-v17-all-charsets-italic.woff2

...al/de/book/fonts/open-sans-v17-all-charsets-regular.woff2

.../de/book/fonts/source-code-pro-v11-all-charsets-500.woff2

documentation/manual/de/book/highlight.css

documentation/manual/de/book/highlight.js

documentation/manual/de/book/imprint.html

documentation/manual/de/book/index.html

documentation/manual/de/book/mark.min.js

documentation/manual/de/book/mdbook-admonish.css

documentation/manual/de/book/mermaid-init.js

documentation/manual/de/book/mermaid.min.js

documentation/manual/de/book/mode-rust.js

documentation/manual/de/book/print.html

documentation/manual/de/book/searcher.js

documentation/manual/de/book/searchindex.js

documentation/manual/de/book/searchindex.json

documentation/manual/de/book/theme-dawn.js

documentation/manual/de/book/theme-tomorrow_night.js