The deeplink-driven plugin install flow shipped in #89464 (salvage of
#82735 by @serefyarar) had no docs. Adds:
- user-guide/features/plugins.md: "One-click install links (Desktop)"
section under Managing plugins — link forms (repo/enable/force), the
confirm-first dialog contract (never auto-installs, same install-time
security scanning as the CLI), hybrid-repo behavior, legacy
plugin-agent/plugin-desktop routing, hermes-dev:// in dev builds, and
the no-SDK anchor example. Cross-links the MCP "Add to Hermes link"
equivalent.
- developer-guide/desktop-plugin-sdk.md: "Distributing with an install
link" section so plugin authors find the link form next to the
packaging docs.