Vendor helgoboss/helgobox (ReaLearn) as basis for custom UI fork

Stripped upstream git history; starting point for replacing the native
SWELL/Win32 mapping UI with something more suited to bulk editing.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

plugin-reaper-realearn/doc/realearn/modules/ROOT/pages/user-interface/settings-dialog.adoc

@@ -0,0 +1,20 @@
+= Settings dialog
+
+include::partial$available-in-app.adoc[]
+
+This dialog opens when pressing the xref:helgobox:ROOT:app/user-interface/title-bar.adoc#title-bar-settings[] button in the title bar and navigating to the ReaLearn section.
+
+image::generated/screenshots/main/settings.png[]
+
+[#controllers]
+== Controllers
+
+Clicking one of the controllers opens the corresponding xref:user-interface/controller-dialog.adoc[].
+
+include::partial$generated/elements/settings/controllers/add.adoc[]
+
+include::partial$generated/elements/settings/controllers/delete.adoc[]
+
+== Related videos
+
+video::tkyNCGOVumw[youtube]