feat: `ssskit-cli`

[lonerapier]

A CLI tool enables end-users and developers to quickly split and recover secrets without writing Rust code.

Approach

• Create a ssskit-cli crate within the workspace.
• Use clap or argh for argument parsing.
• Commands:
  • split --threshold 3 --shares 5 --input secret.txt --out-dir shares/
  • recover --input shares/ --output secret.txt
  • reshare --input shares/ --outputs new_shares/
• Support base64/hex encoding and --json output.
• Integrate serialization module