contrib: add desktop file #902

1. 
   prusnak commented at 11:41 am on October 12, 2025: contributor

   from https://github.com/bitcoin-core/packaging

   => https://github.com/bitcoin-core/packaging/blob/main/debian/bitcoin-qt.desktop

   this simplifies packaging, because currently one needs to fetch a desktop file from another repo instead of using just the main source code one

2. contrib: add desktop file

   from https://github.com/bitcoin-core/packaging
   
   (debian/bitcoin-qt.desktop)

   1c17bd9412
3. 
   DrahtBot commented at 11:41 am on October 12, 2025: contributor

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