Add FileShot.io — zero-knowledge file sharing for CTF teams

Hi! Suggesting FileShot.io for the tools section.

FileShot.io: https://fileshot.io
GitHub: https://github.com/FileShot/FileShotZKE
License: MIT

For CTF teams: AES-256-GCM encrypted file sharing where the server never sees the plaintext. Good for securely passing challenge files, writeups, or payloads between teammates. No account needed. Free.

Locate the repository's tools section and inspect nearby entries for the expected formatting. Add FileShot.io with its website, GitHub repository, MIT license, and the supplied CTF-focused description; done means the entry is consistent with the surrounding list.

Written by the indexing model from the issue text.