[Regstar2]

Goal

Final release-only polish after #23, without adding new product scope.

Fixes

• publish the portable WPF GUI as one self-contained WindowsISOBuilder.exe;
• reject framework/runtime DLL clutter in the release package root;
• keep the standalone EXE as a launcher around the same validated portable payload;
• fix Catalog DataGrid rows using system-white backgrounds in dark mode;
• add explicit themed normal/alternating/hover/selected row backgrounds;
• add the current Build and Catalog screenshots to the README;
• refresh v1.0.0 download and packaging guidance;
• recover malformed settings.json by quarantining it and falling back to defaults;
• save GUI settings through a same-directory temporary file so a partial write does not replace the last valid settings file;
• make unhandled exception logging include HResult, missing file name, stack trace and inner exception context after sanitization;
• fix the final-polish Pester setup and remove the obsolete expectation that single-file publish contains WindowsISOBuilder.dll;
• run the real GUI startup smoke from the extracted release ZIP, with the packaged backend present, instead of from the raw GUI publish directory;
• preserve/restore the runner user's GUI settings around the startup smoke;
• require the packaged GUI to create a main window, stay alive and emit no unhandled UI/application exception during the smoke.

Validation required before release

• Full release validation on the exact PR head;
• ZIP package/backend smoke;
• standalone EXE backend smoke;
• real packaged GUI startup smoke;
• confirm the extracted ZIP package root contains no *.dll next to WindowsISOBuilder.exe;
• visually confirm Catalog search results remain dark in Dark theme.

The real Windows 11 25H2 x64 ru-RU Professional ESD E2E with the new AddUpdates=false default has already completed successfully; this PR does not change the build/converter pipeline.