Add discovery draft spec writer (#134)

[Dimwiddle]

Description

Implement Phase 2 draft markdown writing for discovery output and parser-safe _discovered staging.

This change adds generate_draft_specs() to convert DraftFeature/DraftScenario data into SpecLeft markdown files and updates parser recursion to skip underscore-prefixed directories.

Type of Change

• New feature
• Tests
• Documentation update

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Testing

• make lint-fix
• make lint
• make test
• make pre-commit

Related Issues

Closes #134