feat: jfif/jpe/wbmp format destegi, pencere cascade yerlesimi, konum kaydi duzeltmesi

- file_handler/image_manager: jfif, jpe, wbmp uzantilari
- .desktop + install.sh MimeType: image/vnd.wap.wbmp eklendi
- main.dart: yeni pencere oncekinin saginda acilir (screen_retriever ile ekran tespiti)
- viewer_screen: 2sn polling kaldirildi, konum kaydi tek akisa oturtuldu (acilis + move/resize debounce + close senkron)
- dist/rebuild-deb.sh: .desktop kaynaktan kopyalanir (MimeType/StartupWMClass guncel kalir)
- .deb guncellendi, docs: session-2026-08-03 + plan dokumanlari

lib/services/image_manager.dart

@@ -21,7 +21,7 @@ class ImageManager extends ChangeNotifier {
   void addImages(List<String> paths) {
     final validPaths = paths.where((p) {
       final ext = p.toLowerCase().split('.').last;
-      const supported = ['png', 'jpg', 'jpeg', 'webp', 'bmp', 'gif'];
+      const supported = ['png', 'jpg', 'jpeg', 'jfif', 'jpe', 'webp', 'bmp', 'gif', 'wbmp'];
       return supported.contains(ext) && File(p).existsSync();
     }).toList();