refactor: rename extensions to all-* / stack-* taxonomy

[ulises-jeremias]

Summary

• Rename universal overlays to all-* folders; FastAPI-coupled overlays to fastapi-*
• Split Docker into fastapi-docker, django-docker, celery-docker
• Update templates.json, CI profiles, and slug references in docs/README
• Breaking: remove legacy python-* / github-setup folder paths (no BC shims)

Stack

PR 1/3 of remaining maturity stack (authoring docs already landed on main).

1. This PR — extension taxonomy rename + catalog/CI
2. django-api quality uplift (depends on this)
3. celery-worker / cli-starter / uv-workspace-starter uplift

Sibling consumer PRs (CLI + website) should merge after this lands.

Test plan

• python scripts/ci/validate-registry.py → 5 templates, 10 extensions
• Confirm no extensions/python-* directories remain
• CI matrix profiles use new slugs (fastapi-docker, django-docker, celery-docker, postgres, development-container)

Made with Cursor

[ulises-jeremias]

Stack links

1. Authoring docs already on main (bbaa4df)
2. This PR — extension taxonomy
3. feat(django-api): raise template to FastAPI/CNA quality bar #64 — django-api uplift
4. feat(templates): raise celery, CLI, and uv-workspace to quality bar #65 — celery/cli/uv uplift

Consumers:

• chore: update fixtures for CNA-parity extension slugs create-python-app#213
• chore: update recipes/docs for CNA-parity extension slugs website#7
• chore: use fastapi-docker in profile README example .github#2

@coderabbitai review

[ulises-jeremias]

Review fixes (self-review follow-up)

• Squashed to a single commit
• celery-docker now includes Redis; env vars use BROKER_URL / RESULT_BACKEND (parity with worker/config.py)
• CI enforces extension folder naming law (all-* / {stack}-*, no python-*)
• AUTHORING: incompatibleWith guidance for path-colliding overlays

@coderabbitai review