wiki: sync with docs - bash install scripts + new Install-Scripts pages (EN + DE)
wiki: sync with docs - install script sections (client + server app), EN + DE
wiki: replace emoji markers with text EN/DE labels for cross-platform rendering
wiki: add custom sidebar and header, unify German page naming (-de suffix), add per-page language switchers
Add FlutCloud Nextcloud app docs (install, API) - EN + DE