Run integration tests on all platforms (Linux, macOS, Windows)

Use matrix strategy to test on ubuntu-latest, macos-latest,
and windows-latest. Linux uses xvfb for headless display.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: MarkJamesHoward

.github/workflows/electron-build.yml

@@ -107,7 +107,11 @@ jobs:
 
   test-integration:
     needs: build
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
 
     steps:
       - uses: actions/checkout@v4
@@ -130,10 +134,16 @@ jobs:
         working-directory: electron
         run: npm run build
 
-      - name: Run integration tests
+      - name: Run integration tests (Linux)
+        if: runner.os == 'Linux'
         working-directory: electron
         run: xvfb-run --auto-servernum npm run test:integration
 
+      - name: Run integration tests (macOS/Windows)
+        if: runner.os != 'Linux'
+        working-directory: electron
+        run: npm run test:integration
+
   test-linux-install:
     needs: build
     runs-on: ubuntu-latest