When the user has both Hellion Chat and upstream Chat 2 installed and
loaded, the parallel chat-window replacement and Hook collisions can
crash FFXIV at frame boundaries. The new detector inspects
IDalamudPluginInterface.InstalledPlugins and throws an
InvalidOperationException with a localized message if Chat 2 is loaded,
which Dalamud surfaces cleanly instead of letting the load proceed
into a runtime crash.
Bilingual messages (EN/DE) follow the existing HellionStrings pattern.
