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/.github/actions/check/action.yml

@@ -0,0 +1,30 @@
+name: Check
+description: Check Rust code via Clippy
+inputs:
+  args:
+    description: 'Cargo arguments'
+    required: false
+    default: ''
+runs:
+  using: "composite"
+  steps:
+    - name: Install Rust
+      uses: dtolnay/rust-toolchain@1.84.0
+      with:
+        components: clippy
+
+    - name: Set up dependencies
+      if: runner.os == 'Linux'
+      run: |
+        sudo apt-get update
+        sudo apt-get install nasm php libudev-dev libxdo-dev libx11-dev  libxcursor-dev libxcb-dri2-0-dev libxcb-icccm4-dev libx11-xcb-dev mesa-common-dev libgl1-mesa-dev libglu1-mesa-dev libspeechd-dev libgtk-3-dev
+      shell: sh
+
+    - name: Rust cache
+      uses: swatinem/rust-cache@v2
+
+    - name: cargo clippy
+      env:
+        ARGS: ${{ inputs.args }}
+      run: cargo clippy $ARGS -- -D warnings
+      shell: sh