feat: add integration tests for build artifacts

Validate deb, rpm, and appimage packages after build in CI.
Tests verify package metadata, file layout, desktop entries,
icons, launcher scripts, asar contents (frame-fix, cowork,
native stub, tray icons), and --doctor smoke tests.

Runs as a reusable workflow with matrix strategy (one job per
format) between build and release jobs, gating releases on
passing artifact validation.

.github/workflows/ci.yml

@@ -49,6 +49,11 @@ jobs:
       artifact_suffix: ${{ matrix.artifact_suffix }}
       release_tag: ${{ startsWith(github.ref, 'refs/tags/v') && github.ref_name || '' }}
 
+  test-artifacts:
+    name: Test Build Artifacts
+    needs: [build-amd64]
+    uses: ./.github/workflows/test-artifacts.yml
+
   build-arm64:
     name: Build Packages (arm64 - ${{ matrix.artifact_suffix }})
     needs: test-flags
@@ -76,7 +81,7 @@ jobs:
   release:
     name: Create Release
     if: startsWith(github.ref, 'refs/tags/v')
-    needs: [test-flags, build-amd64, build-arm64]
+    needs: [test-flags, build-amd64, build-arm64, test-artifacts]
     runs-on: ubuntu-latest
     permissions:
       contents: write

.github/workflows/test-artifacts.yml

@@ -0,0 +1,50 @@
+name: Test Build Artifacts (Reusable)
+
+on:
+  workflow_call:
+  workflow_dispatch:
+
+jobs:
+  test-artifact:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - format: deb
+            artifact: package-amd64-deb
+            container: ""
+          - format: rpm
+            artifact: package-amd64-rpm
+            container: "fedora:42"
+          - format: appimage
+            artifact: package-amd64-appimage
+            container: ""
+
+    name: Validate ${{ matrix.format }} package
+    runs-on: ubuntu-latest
+    container: ${{ matrix.container || '' }}
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Download artifact
+        uses: actions/download-artifact@v4
+        with:
+          name: ${{ matrix.artifact }}
+          path: artifacts/
+
+      - name: Install test dependencies (Fedora)
+        if: matrix.format == 'rpm'
+        run: dnf install -y findutils file nodejs npm
+
+      - name: Install test dependencies (Ubuntu)
+        if: matrix.format != 'rpm'
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y file libfuse2
+
+      - name: Run artifact tests
+        run: |
+          chmod +x tests/test-artifact-${{ matrix.format }}.sh
+          tests/test-artifact-${{ matrix.format }}.sh artifacts/