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/playtime-clip-engine-placeholder/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "playtime-clip-engine"
+version = "0.1.0"
+authors = ["Benjamin Klum <benjamin.klum@helgoboss.org>"]
+edition = "2021"
+publish = false
+
+[features]
+licensing = []