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

@@ -76,7 +76,22 @@ Go to [this repository](https://github.com/ScanTailor-Advanced/scantailor-libs-b
 
 **Linux – Wayland (issue #97):** If you see rendering issues (blank or corrupted windows) when running under Wayland, try starting the application with `QT_QPA_PLATFORM=xcb` to use the X11 compatibility layer.
 
-**Linux – Flatpak / Flathub (issue #105):** A Flatpak manifest is provided in `flatpak/org.scantailor.Advanced.json`. To build locally: `flatpak-builder --user --force-clean build flatpak/org.scantailor.Advanced.json` (requires `flatpak` and `flatpak-builder`). To publish on Flathub, use a distinct application ID (e.g. `org.scantailor.Advanced`) so it does not conflict with the original ScanTailor package.
+**Linux – Flatpak / Flathub (issue #105):**
+
+- **This repository:** a Flatpak manifest lives at [`flatpak/org.scantailor.Advanced.json`](flatpak/org.scantailor.Advanced.json) (application ID `org.scantailor.Advanced`). Install the KDE 5.15 runtime and SDK branch **`5.15-23.08`** from Flathub, then build (and optionally install) with `flatpak-builder` (requires `flatpak` and `flatpak-builder`):
+
+  ```bash
+  flatpak install flathub org.kde.Platform//5.15-23.08 org.kde.Sdk//5.15-23.08
+  flatpak-builder --user --install-deps-from=flathub --install --force-clean build-dir flatpak/org.scantailor.Advanced.json
+  ```
+
+  To build without installing, omit `--install`. If your `flatpak-builder` is too old for `--install`, use a local directory repository (see the [flatpak-builder documentation](https://docs.flatpak.org/en/latest/flatpak-builder.html)).
+
+- **Flathub today:** the published Flatpak still tracks the **original** repository ([`com.github._4lex4.ScanTailor-Advanced`](https://flathub.org/apps/com.github._4lex4.ScanTailor-Advanced) on Flathub). Building from this manifest does **not** change that listing.
+
+- **Future work:** listing **this** fork on Flathub needs a **separate** submission under the Flathub process (application ID, new or migrated package on `github.com/flathub`, maintainer agreement). Track that in [issue #105](https://github.com/ScanTailor-Advanced/scantailor-advanced/issues/105).
+
+**Linux – GitHub Releases (.deb / AppImage, issue #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. Report problems with those binaries in [issue #64](https://github.com/ScanTailor-Advanced/scantailor-advanced/issues/64).
 
 ## About this fork
 

build-deb.sh

@@ -56,13 +56,14 @@ 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/4lex4/scantailor-advanced
+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

flatpak/org.scantailor.Advanced.json

@@ -1,10 +1,8 @@
 {
   "id": "org.scantailor.Advanced",
   "runtime": "org.kde.Platform",
-  "runtime-version": "5.15-22.08",
+  "runtime-version": "5.15-23.08",
   "sdk": "org.kde.Sdk",
-  "base": "org.kde.Sdk",
-  "base-version": "5.15-22.08",
   "command": "scantailor",
   "finish-args": [
     "--share=ipc",