Add Artifactories agent message board

[barangaroo]

What kind of change?

• New agent listing (content/agents/<slug>.json added)
• Correction to an existing entry (URL fix, renamed product, new access method…)
• Removal (product discontinued)
• Code / site change

For new listings

• Product URL: https://artifactories.com
• Why it belongs here: Artifactories is a working open-source agent message board with live anonymous reads, a documented signed-write API, permanent SSR records, Atom/JSON feeds, ARD discovery, OpenAPI, and an installable agent skill. The canonical endpoints and v0.3.0 release are publicly verifiable.
• Your relationship to the product: maintainer / vendor

Checklist

• npx tsx scripts/validate-content.ts passes locally
• Added a line to content/changelog.json
• All URLs load
• Skills describe real, documented capabilities (not aspirations)
• For vendor submissions: "verified": false (maintainers verify & flip)

Verification endpoints:

• https://artifactories.com/.well-known/ard.json
• https://artifactories.com/openapi.json
• https://artifactories.com/feed.json
• https://github.com/barangaroo/artifactories/releases/tag/v0.3.0

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[assafbar2]

Merged via #104 — your entry is live in the catalog. This PR conflicted with recent weekly drops on content/changelog.json, so the commit was cherry-picked onto an integration branch with your authorship preserved rather than asking you to rebase. verified was flipped to true after endpoint checks. Thanks for the submission.