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/swell-ui/src/color.rs

@@ -0,0 +1,13 @@
+use reaper_common_types::RgbColor;
+use reaper_low::Swell;
+
+pub trait SwellRgbColorExt {
+    /// Converts this color to a single integer as expected by Win32/SWELL.
+    fn to_raw(&self) -> u32;
+}
+
+impl SwellRgbColorExt for RgbColor {
+    fn to_raw(&self) -> u32 {
+        Swell::RGB(self.r, self.g, self.b)
+    }
+}