Add a Windows desktop installer for PC-based OmniNX installs.

This lets mass deployments and modchip setups apply the same install/update flow from a PC, with generated deletion lists kept in sync with the payload headers.

.github/workflows/build-desktop.yml

@@ -0,0 +1,44 @@
+name: Build Desktop Installer
+
+on:
+  push:
+    paths:
+      - 'desktop/**'
+      - 'source/deletion_lists_*.h'
+      - 'tools/generate_deletion_lists.py'
+      - '.github/workflows/build-desktop.yml'
+  workflow_dispatch:
+
+jobs:
+  build:
+    name: Build (${{ matrix.rid }})
+    runs-on: windows-latest
+    strategy:
+      matrix:
+        rid: [win-x64, win-arm64]
+
+    steps:
+      - uses: actions/checkout@v5
+
+      - name: Setup .NET
+        uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: '8.0.x'
+
+      - name: Generate deletion lists
+        run: python tools/generate_deletion_lists.py
+
+      - name: Publish
+        run: >
+          dotnet publish desktop/OmniNX.DesktopInstaller/OmniNX.DesktopInstaller.csproj
+          -c Release
+          -r ${{ matrix.rid }}
+          -p:SelfContained=false
+          -p:PublishSingleFile=true
+          -o desktop/out/${{ matrix.rid }}
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: OmniNX-Desktop-Installer-${{ matrix.rid }}
+          path: desktop/out/${{ matrix.rid }}/OmniNX-Desktop-Installer.exe