Add SiliSim

[ViezeVingertjes]

Summary

• Adds SiliSim, a 2D silicon logic simulator for learning and building digital circuits.
• AppImage is hosted at a stable URL: https://silisim.com/downloads/silisim-linux-x86_64.AppImage

AppImage details

• Includes AppStream metainfo (com.silisim.SiliSim.appdata.xml)
• Desktop entry passes desktop-file-validate
• Works offline (native desktop app, no network required)
• Passes appdir-lint.sh locally

Test plan

• CI automated review passes (green check)
• Screenshot is captured from the running AppImage

[ViezeVingertjes]

Pushed an empty commit to retrigger CI.

The previous test runs were cancelled after hitting the workflow timeout-minutes: 10 limit (see run annotations), not because worker.sh reported an AppImage failure. Happy to adjust anything on the SiliSim side if a future run fails with a concrete error.