Update development status classifier for 1.0

## Problem

`pyproject.toml` has the development status classifier set to Alpha:

```toml
classifiers = [
    "Development Status :: 3 - Alpha",
    ...
]
```

## Solution

For a 1.0 release, update to Production/Stable:

```toml
classifiers = [
    "Development Status :: 5 - Production/Stable",
    ...
]
```

This tells PyPI users that the package is ready for production use.

