Upstream moved the documentation sources from doc/ to docs/ (#7584), so the
page this branch adds now belongs under docs/doxygen/pages/user_documentation/
gameplay/. The index.md edit auto-merged onto the moved file, but the new page
stayed at the old path, and GitHub's merge engine reported a conflict in
index.md because the file it edits was deleted upstream.
No source changes: the merge is upstream/master as-is plus the doc relocation.
Rename doc/ to docs/ so GitHub picks up docs/CONTRIBUTING.md and Doxygen keeps including it, and update all references to the old layout:
- Doxygen output now goes to docs-output/, exposed by .gitignore
- docs workflow triggers on docs/** and publishes docs-output/html
- theme submodule moved to docs/doxygen/theme
- schema URLs in both XML parsers point at docs/xsd/
- README, developer docs, desktop workflow filters, .dockerignore and gcovr config updated for the new paths
The v3 card database schema is kept as docs/xsd/cards_v3.xsd.
