[mmattel]

This is the migration of the developer documentation from the ocis repo into this documentation repo. Everything is now fully integrated in the Antora framework.

Without going into the details, the migration was a massive change, but now everything is consistent, clear in the setup and commented where required. The Claude/AGENTS files have been updated so others benefit from the work done.

Post merging, we can:

• Retire the owncloud.dev homepage and do a full redirect to doc.owncloud.com
• The docs/ content in the ocis repo is now obsolete, but this needs checking before removal
• If possible, we can retire the owncloud.github.io repo as this is imho no longer used - to be checked.
  This was the repo holding the hugo framework that was required building owncloud.dev

IMPORTANT: there is no forwarding of content from the old web page possible, this is a breaking change !!

Note that this PR also fully integrates the Swagger-UI (LibgeGraph) and the ocis-php-sdk documentation. 😄

Tasks post merging:

• ocis developers MUST cross read, pls also double check the releasing guide if the steps match the required procedures (this starts in the root of the documentation
• web developers MUST cross read the web documentation which can be found in the client section (starts in the root)

[LukasHirt]

Marking this like this just to prevent merge before the llm js changes are moved to a separate PR since this PR is focused on dev docs - not on internal tooling. Already working on the split now.

[LukasHirt]

PR with the llms.txt changes: #156