fix: document id add_members resulting in a snake case url instead of kebap case

[AlexAndBear]

https://docs.opencloud.eu/docs/next/user/spaces/add_members -> must be https://docs.opencloud.eu/docs/next/user/spaces/add-members

[Copilot]

Pull request overview

This PR standardizes the document ID from add_members to add-members across all versions and localizations of the "Add members" documentation, and updates the homepage to dynamically generate documentation paths based on the user's preferred version.

Changes:

• Updated document ID from underscore to hyphen format (add_members → add-members) for consistency
• Added dynamic version-aware path generation for documentation links on the homepage
• Applied changes consistently across all language versions and documentation versions

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
versioned_docs/version-4.0/user/spaces/add-user.md	Changed document ID to use hyphen format
src/pages/index.tsx	Added version-aware path generation using useDocsPreferredVersion hook
i18n/de/docusaurus-plugin-content-docs/version-4.0/user/spaces/add-user.md	Changed document ID to use hyphen format (German version)
i18n/de/docusaurus-plugin-content-docs/current/user/spaces/add-user.md	Changed document ID to use hyphen format (German current version)
docs/user/spaces/add-user.md	Changed document ID to use hyphen format (main docs)

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.