Org-level special repo for 3dl-dev. Its only job is the org profile.

• profile/README.md renders as the landing page at github.com/3dl-dev.

Keep it aligned with the website. The project showcase here mirrors the "What we're building" section on 3dl.dev (repo 3dl-dev/website, index.html): same groups, blurbs, and links. Change one, change the other in the same session. No em-dashes.