Add Rust/Cargo integration example

[HMAKT99]

Summary

AKF has Python and TypeScript SDKs, but many AI/ML tools are written in Rust. A Rust example showing how to read/write AKF metadata would expand the ecosystem.

What needs to happen

1. Create examples/rust/ directory
2. Add a simple Rust program that reads an AKF JSON sidecar and prints trust scores
3. Add a Cargo.toml with serde_json for parsing
4. Include a README with usage instructions

Helpful context

• AKF metadata is just JSON — no special library needed, just serde_json
• See spec/akf-v1.1.schema.json for the schema
• Look at examples/ for existing examples in other languages

Acceptance criteria

• cargo run reads and prints AKF metadata from a .akf file
• README explains usage