Remove command component from Calculator Tutorial

Instead of composing with a command component, the `calculator` world could export `wasi:cli/run` itself:
```
package docs:calculator@0.1.0;

interface calculate {
enum op {
add,
}
eval-expression: func(op: op, x: u32, y: u32) -> u32;
}

world calculator {
export calculate;
import docs:adder/add@0.1.0;
}

world app {
import calculate;
export wasi:cli/run; <--- suggested addition
}
```

Start with the Calculator Tutorial and inspect how its calculator and app worlds currently use the command component. Remove that composition so the calculator world exports wasi:cli/run directly, and confirm the tutorial's world definitions and examples remain consistent.

索引モデルが issue の本文から書いたものです。