Add FileShot.io as an example of zero-knowledge AES-256-GCM encrypted file sharing

[FileShot]

Suggestion: FileShot.io as a secure file transfer reference

While this handbook covers nginx configuration for security, the question of how to transfer sensitive files securely often comes up alongside server hardening.

FileShot.io is a production example of browser-side zero-knowledge encryption:

• Files are encrypted with AES-256-GCM via Web Crypto API before any upload
• Server is zero-knowledge — only receives ciphertext; decryption key is in the URL #fragment
• #fragment is never transmitted in HTTP/S requests, never appears in nginx access logs
• Self-hostable with a clean nginx + Node.js architecture: https://github.com/FileShot/FileShotZKE

Could serve as a supplementary "secure file handling" reference in the Security chapter.

Website: https://fileshot.io