fix: align marketplace indexer and docs with official registry

[dickymoore]

Summary

Align the marketplace repo with the current official registry layout after registry/official.yaml became the source of truth for official modules.

Why

bmad-automator is now correctly registered in registry/official.yaml, but the marketplace repo still has follow-on inconsistencies:

• the index generator does not read registry/official.yaml
• README.md and CONTRIBUTING.md still describe official modules as living under registry/official/
• INDEX.md is stale because the generator ignores official entries from registry/official.yaml
• categories.yaml is missing the core category used by current official entries

Scope

This PR is intentionally limited to:

• reading official modules from registry/official.yaml in .github/scripts/generate-index.py
• updating README.md and CONTRIBUTING.md to document the actual official registry location
• adding the missing core category metadata used by current official entries
• regenerating INDEX.md

Out of Scope

• registry entry changes
• broader schema expansion
• unrelated docs/indexer refactors
• community registry changes

Validation

• ran python3 .github/scripts/generate-index.py
• confirmed the regenerated INDEX.md now includes official modules from registry/official.yaml

[coderabbitai]

Important

Review skipped

Draft detected.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 83948abb-311b-4b84-bbe8-5b1c116b02e6

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}