Mark all pages in docs/plugins/ with legacy admonition banners pointing
to the appropriate new frontend system and backend system documentation.
Rename the sidebar section to "Plugins (Legacy)" and move it lower in
the navigation hierarchy. Add cross-references from the new frontend
system building-plugins guide to relevant cross-cutting topics (i18n,
analytics, feature flags, search) that still live in the legacy section.
Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
Made-with: Cursor
Patrik Oldsberg
35e130c601