Fix Linux release packaging and document Flatpak (#64, #105)

- release.yml: bundle Qt via linuxdeploy --plugin qt for AppImage xcb
- build-deb.sh: point Maintainer, Homepage, Bugs at ScanTailor-Advanced fork
- flatpak: KDE runtime 5.15-23.08, drop redundant base/base-version
- README: Flatpak/Flathub scope, local build steps, Releases pointer for #64

Author: pablogventura

.github/workflows/release.yml

@@ -81,7 +81,8 @@ jobs:
         run: |
           cd build-appimage
           export QMAKE=/usr/bin/qmake
-          ../linuxdeploy-x86_64.AppImage --appdir AppDir -e AppDir/usr/bin/scantailor --output appimage
+          # Bundle Qt platform plugins (e.g. xcb) via linuxdeploy-plugin-qt; same-dir discovery.
+          ../linuxdeploy-x86_64.AppImage --appdir AppDir --plugin qt -e AppDir/usr/bin/scantailor --output appimage
           OUT=$(ls -1 *.AppImage 2>/dev/null | head -1)
           mv "$OUT" "../scantailor-advanced-${{ github.ref_name }}-x86_64.AppImage"
 

README.md

@@ -87,6 +87,8 @@ Go to [this repository](https://github.com/ScanTailor-Advanced/scantailor-libs-b
 
 **Application ID:** the manifest uses `org.scantailor.Advanced` so it does **not** replace the legacy `com.github._4lex4.*` Flatpak. Author docs: [for app authors](https://docs.flathub.org/docs/for-app-authors/).
 
+**Linux – GitHub Releases (.deb / AppImage, [issue #64](https://github.com/ScanTailor-Advanced/scantailor-advanced/issues/64)):** Version tags matching `v*` run [`.github/workflows/release.yml`](.github/workflows/release.yml), which produces a `.deb` ([`build-deb.sh`](build-deb.sh)) and an AppImage attached to the GitHub Release when the workflow is enabled. Report problems with those binaries in [issue #64](https://github.com/ScanTailor-Advanced/scantailor-advanced/issues/64).
+
 **Community examples / test data:** See also [scantailor-testing](https://github.com/ImageProcessing-ElectronicPublications/scantailor-testing) (community repository; issue [#43](https://github.com/ScanTailor-Advanced/scantailor-advanced/issues/43)).
 
 ## About this fork

build-deb.sh

@@ -58,13 +58,14 @@ Section: graphics
 Priority: optional
 Architecture: ${ARCH}
 Depends: ${DEPS}
-Maintainer: 4lex4 <4lex49@zoho.com>
+Maintainer: ScanTailor-Advanced <https://github.com/ScanTailor-Advanced/scantailor-advanced>
 Description: Interactive post-processing tool for scanned pages
  ScanTailor Advanced merges features from ScanTailor Featured and Enhanced,
  with improvements for page splitting, deskewing, content selection,
  margins, dewarping and output. Supports batch processing and multiple
  output formats.
 Homepage: https://github.com/ScanTailor-Advanced/scantailor-advanced
+Bugs: https://github.com/ScanTailor-Advanced/scantailor-advanced/issues
 EOF
 
 # Optional: refresh icon and desktop caches after install