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/post-checkout/action.yml

@@ -0,0 +1,24 @@
+name: Post-checkout
+description: Checkout with Playtime Engine
+inputs:
+  playtime-engine-deploy-key:
+    description: 'Playtime Engine deploy key'
+    required: true
+  license-processor-deploy-key:
+    description: 'License Processor deploy key'
+    required: true
+runs:
+  using: "composite"
+  steps:
+    # Checkout with Playtime Engine
+    - name: Setup ssh-agent
+      uses: webfactory/ssh-agent@v0.7.0
+      with:
+        ssh-private-key: |
+          ${{ inputs.playtime-engine-deploy-key }}
+          ${{ inputs.license-processor-deploy-key }}
+
+    - name: Update submodules
+      run: |
+        git submodule update --init
+      shell: sh