Add cert-depot to Tools section

[dimastopel]

Add cert-depot — a free, open-source self-signed SSL/TLS certificate generator.

• Written in Go, ships as a single binary with no external dependencies
• Uses Go's native crypto/x509 (no OpenSSL)
• Keys are generated in memory and streamed directly to the user — nothing is stored on the server
• Supports RSA 2048/4096, ECDSA P-256/P-384, Subject Alternative Names
• ZIP (PEM) and PFX (PKCS#12) output
• MIT licensed

Live instance: https://cert-depot.com