Fix AppImage build: valid desktop Categories and non-deprecated plugin vars

appimagetool rejects the unregistered "Design" category; keep
Graphics;2DGraphics. Use LDAI_OUTPUT/TAG so the appimage plugin no longer
warns about the deprecated OUTPUT/VERSION variables.

Author: skvggor

.github/workflows/release.yml

@@ -57,17 +57,18 @@ jobs:
           # Icon basename must match Icon= in the .desktop file.
           cp assets/icons/icon-256.png article-cover-art-generator.png
 
-          export OUTPUT="acag-${VERSION}-x86_64.AppImage"
+          # LDAI_OUTPUT is the plugin's own (non-deprecated) output-name var.
+          export LDAI_OUTPUT="acag-${TAG}-x86_64.AppImage"
           ./linuxdeploy.AppImage \
             --appdir AppDir \
             -e target/release/acag \
             -d assets/article-cover-art-generator.desktop \
             -i article-cover-art-generator.png \
             --output appimage
 
-          mv "${OUTPUT}" dist/
+          mv "${LDAI_OUTPUT}" dist/
         env:
-          VERSION: ${{ github.ref_name }}
+          TAG: ${{ github.ref_name }}
 
       - name: Publish to release
         uses: softprops/action-gh-release@v2

assets/article-cover-art-generator.desktop

@@ -6,6 +6,6 @@ Comment=Generate 1:1 article cover art in an Omakase style
 Exec=acag
 Icon=article-cover-art-generator
 Terminal=false
-Categories=Graphics;2DGraphics;Design;
+Categories=Graphics;2DGraphics;
 Keywords=acag;cover;art;svg;png;article;generator;omakase;
 StartupNotify=true