Submission: Add kbCalc (PR creation is limited to collaborators)

Hi! I'd like to submit **kbCalc** to the apps list, but opening a pull request on this repository is currently limited to collaborators, so I'm filing the submission as an issue instead.

**kbCalc** — an open source (MIT) floating, translucent calculator with a built-in Winamp-style MP3 player, built on Electron (one codebase for Windows, Linux and macOS): real-time visualizer, 5-band equalizer, named playlists, ID3 tags, podcasts, internet radio.

- Repository: https://github.com/tengolabs/kbcalc
- Installers for all three OSes: https://github.com/tengolabs/kbcalc/releases

A ready-made branch with the standard submission (`apps/kbcalc/kbcalc.yml` + 1024×1024 `kbcalc-icon.png`, authored per contributing.md) is here and can be pulled or cherry-picked directly:
https://github.com/electron/apps/compare/main...tengosro:kbcalc

If you prefer a PR and can allow it, happy to open one. Thanks!

Start by reading contributing.md and reviewing the ready-made comparison branch. Check apps/kbcalc/kbcalc.yml and the 1024×1024 kbcalc-icon.png against the submission requirements, then confirm the kbCalc repository and releases links work. Done means the standard app listing and icon are accepted for inclusion.

Written by the indexing model from the issue text.