feat: use imajviewericon.png as app icon for both Linux and Windows

- Replace generated icon in install.sh with proper imajviewericon.png (64x64 resize)
- Update deb/ icon to match source icon (64x64 PNG)
- Update windows/runner/resources/app_icon.ico from imajviewericon.png (6 sizes: 16-256)
- Add SetupIconFile to Inno Setup installer config

windows/installer.iss

@@ -23,6 +23,7 @@ SolidCompression=yes
 WizardStyle=modern
 PrivilegesRequired=admin
 ArchitecturesInstallIn64BitMode=x64compatible
+SetupIconFile=..\windows\runner\resources\app_icon.ico
 
 [Languages]
 Name: "turkish"; MessagesFile: "compiler:Languages\Turkish.isl"