Encrypted mnemonics

[kingonly]

The mnemonics are now stored in plain text which is vulnerable to a malicious attack. We need to encrypt them with either:

• Passkey
• Web Crypto
• PIN code
  Let's research these options, pros and cons and decide one to implement.

[kingonly]

@erdemyerebasmaz let's give this a try as a fallback: https://claude.ai/public/artifacts/e672b0a7-3f8d-47ea-a37d-addb7ffd6d89