[PictureLoader] Fix custom-folder pictures in subdirectories not loading (#7340)

CardPictureLoaderLocal compared the full file name (including extension)
of the custom-folder candidate against the extension-stripped base name of
each directory entry, so a CUSTOM subfolder image like
pics/CUSTOM/poker/1 of Hearts.png never matched and the card fell through
to the network. Compare the complete base names instead.

Add matcher tests covering CUSTOM subfolder resolution.

Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>

cockatrice/src/interface/card_picture_loader/card_picture_loader_local.cpp

@@ -101,7 +101,7 @@ QImage CardPictureLoaderLocal::tryLoadCardImageFromDisk(const QString &setName,
         for (const QString &path : candidatePaths) {
             QFileInfo fileInfo(path);
             QDir dir = fileInfo.dir();
-            QString baseName = fileInfo.fileName();
+            QString baseName = fileInfo.completeBaseName();
 
             if (!dir.exists()) {
                 continue;