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

install.sh

@@ -74,7 +74,7 @@ Exec=${BIN_LINK} %F
 Icon=${APP}
 Terminal=false
 Categories=Graphics;Viewer;RasterGraphics;
-MimeType=image/png;image/jpeg;image/webp;image/bmp;image/gif;image/jpg;
+MimeType=image/png;image/jpeg;image/webp;image/bmp;image/gif;image/jpg;image/vnd.wap.wbmp;
 StartupNotify=false
 StartupWMClass=com.example.imajviewer
 EOF