ci: add GitHub Actions auto-labeling for PRs

[Rome-1]

What

Add a GitHub Actions workflow that auto-labels PRs based on title prefix and changed files.

Why

As community contributions grow, manual labeling doesn't scale. Auto-labeling helps triagers and contributors see at a glance what a PR does.

Rules

By title prefix:

Prefix	Label
`feat:`	`enhancement`
`fix:`	`bug`
`test:`	`testing`
`docs:`	`documentation`
`pattern:`	`secret-pattern`

By changed files:

Path pattern	Label
`node/src/scanners/secret-patterns.ts`	`secret-pattern`
`python/rafter_cli/scanners/secret_patterns.py`	`secret-pattern`
`recipes/**`	`documentation`
`node/tests/` or `python/tests/`	`testing`

File to create

`.github/workflows/auto-label.yml` — use `actions/labeler@v5` or a simple conditional workflow.

Reference

See https://github.com/actions/labeler for the standard approach.