Add source-first migration tooling for step templates

[bcullman]

Summary

Adds the tooling needed to validate a source-first step-template workflow before submitting the actual repository migration.

Related: #1677

Included in this PR

• migration tooling for moving step-template JSON into a source-first layout
• script extraction tooling for splitting embedded script content into source files
• build integration for regenerating step-templates/*.json from source
• validation tooling to compare generated output with the current JSON workflow
• reset tooling for local migration runs

Intended use

This branch is meant to support validation of the follow-up migration branch.

Use it to:

1. run the migration tooling
2. confirm the generated JSON output matches the current workflow within the known validation exclusions
3. review the resulting source-first layout
4. reset back to the branch baseline if needed

A follow-up PR will use this tooling to submit the actual repository migration and related documentation updates.