[danmar]

Add @2x and @3x icons rendered from the SVG sources of Tango 0.8.90 (the latest Tango release) so the icons are sharp on high-DPI screens. The 22x22 icons are unchanged. Qt picks the @nx files automatically.

Icons that were renamed copies of Tango icons now use the Tango files:

• showerrors.png -> dialog-error.png
• showwarnings.png -> dialog-warning.png
• showperformance.png -> utilities-system-monitor.png
• openproject.png -> folder.png (22x22 instead of a scaled 32x32)
• showstylewarnings.png was unused and is removed

Hand-made icons are replaced:

• "Reanalyze modified files": Refresh file.svg from the Tango project on Wikimedia Commons (public domain)
• "Show Scratchpad": Tango accessories-text-editor

Update the Tango link in AUTHORS, tango.freedesktop.org is gone.

[dmcppcheck]

AI review

I found no problems. The PR only changes GUI resources: PNG files, gui.qrc, mainwindow.ui and AUTHORS. No C++ code changes. Every icon path in the GUI sources points to a file that exists and is listed in gui.qrc. Nothing in the build or in the code still uses the deleted images. The 22x22 icons that were already there are byte-identical to the base. Each @2x/@3x file has exactly 2× or 3× the size of its base icon.

Testing

I did not build or run cppcheck or testrunner, because the PR changes no code they use. The GUI can't be built here, and neither rcc nor uic is installed, so I checked the resources with scripts instead:

• Files listed in gui.qrc: every <file> entry exists in pr/gui/.
• Icon references in the GUI: I collected every :/images/... and :images/... path in gui/*.cpp, *.h and *.ui. All the files exist, and all of them are in gui.qrc.
• Deleted images: I searched the whole tree for view-refresh, showerrors, showstylewarnings, showwarnings, showperformance, openproject.png and scratchpad.png. The only hits are gui/help/tools.html and gui/help/online-help.qhp. They point to the separate screenshot gui/help/images/scratchpad.png, which still exists, so nothing is broken.
• Image sizes: I read each PNG header. All base icons are 22x22, every @2x is 44x44 and every @3x is 66x66. Every chunk CRC of every PNG is valid.
• Old 22x22 icons: I compared them with cmp against base/. None changed.
• Renamed copies: the deleted showerrors.png, showwarnings.png and showperformance.png are byte-identical to dialog-error.png, dialog-warning.png and utilities-system-monitor.png, so on normal-DPI screens those three icons look the same as before.
• XML: gui.qrc and mainwindow.ui both parse as well-formed XML.

What I could not check: how the new icons render in a running GUI, and whether Qt picks up the @2x/@3x files on a high-DPI screen.

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Automated review of 60701a6 by Claude. The pull request was built and tested locally.