fix(ci): Fix AppImage build failures for OCR and HardSubX variants

OCR build fix:
- linuxdeploy was failing with "Invalid magic bytes in file header"
  because it was passed the wrapper script instead of the actual binary
- When OCR is enabled, ccextractor is renamed to ccextractor.bin and
  a wrapper script sets TESSDATA_PREFIX before executing the binary
- Now correctly passes ccextractor.bin to linuxdeploy when it exists

HardSubX build fix:
- Add libavdevice-dev to FFmpeg dependencies in CI workflow
- rusty_ffmpeg requires libavdevice which was missing

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

linux/build_appimage.sh

@@ -203,9 +203,18 @@ esac
 # Build AppImage
 echo "Building AppImage..."
 export OUTPUT="$OUTPUT_NAME"
+
+# Determine which executable to pass to linuxdeploy
+# For OCR builds, we have a wrapper script, so pass the actual binary (.bin)
+if [ -f "AppDir/usr/bin/ccextractor.bin" ]; then
+    LINUXDEPLOY_EXEC="AppDir/usr/bin/ccextractor.bin"
+else
+    LINUXDEPLOY_EXEC="AppDir/usr/bin/ccextractor"
+fi
+
 ./linuxdeploy-x86_64.AppImage \
     --appdir=AppDir \
-    --executable=AppDir/usr/bin/ccextractor \
+    --executable="$LINUXDEPLOY_EXEC" \
     --desktop-file=AppDir/ccextractor.desktop \
     --icon-file=AppDir/ccextractor.png \
     --output=appimage