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/playtime/modules/ROOT/pages/realearn-targets.adoc

@@ -0,0 +1,10 @@
+= ReaLearn targets
+
+[[feature-realearn]]
+xref:realearn::introduction.adoc[ReaLearn] is the controller integration tool at the heart of Helgobox that enables Playtime's _haptic_ features. It drives the xref:user-interface/toolbar.adoc#toolbar-show-hide-midi-triggers[MIDI trigger] functionality, integrates the xref:key-concepts.adoc#grid-controller[grid controllers], and allows you to craft your own controller experiences. ReaLearn is the engine behind it all!
+
+In simple terms, a xref:realearn::key-concepts.adoc#target[ReaLearn target] defines what happens when you press a button on your controller. ReaLearn provides a wide variety of such xref:realearn::targets.adoc[targets], including a xref:realearn::targets/playtime.adoc[specialized set of targets] tailored for Playtime. Most of these targets even support xref:realearn::key-concepts.adoc#feedback[], enabling features like LED lighting or display updates. That gives you the flexibility to create highly customized controller integrations for Playtime!
+
+For a glimpse of what's possible, take a look at Playtime's xref:usage/grid-controllers.adoc[grid controller support]. This functionality isn't hard-coded into Playtime, it's entirely implemented through xref:realearn::further-concepts/compartment.adoc#compartment-preset[ReaLearn compartment presets].
+
+All targets are described xref:realearn::targets/playtime.adoc[here].