Add seekrit to Secret Management

[mileszim]

Adds seekrit at the bottom of Secret Management.

What distinguishes it from the neighbours already in that section: the server stores only ciphertext. Keys are generated and held client-side, so encryption and decryption happen in the CLI, in an egress proxy, or in a read-path SDK — never in the API.

Delivery paths a DevOps reader would care about:

• seekrit run -- <cmd> injects decrypted secrets into a child process's environment (no .env on disk)
• a Rust egress proxy that substitutes {{seekrit:NAME}} placeholders in outbound requests behind a default-deny allowlist, so a workload can call an API without holding the key
• read-path SDKs for Python, Go, JavaScript and Ruby, a GitHub Action, a Terraform provider, and a Helm chart that syncs into Kubernetes through stock External Secrets Operator

Disclosure: I maintain seekrit. Happy to shorten the description if it runs long for the section's style.