Automated SEO fixes: resolve title_too_short on artifacts CLI reference

Update frontmatter title from 'Artifacts' to 'Artifact commands' to meet
the 20-char minimum for <title> tags. Sidebar label remains 'Artifacts'.

Co-Authored-By: Oz <oz-agent@warp.dev>

Author: petradonka

src/content/docs/reference/cli/artifacts.mdx

@@ -1,5 +1,5 @@
 ---
-title: Artifacts
+title: Artifact commands
 description: >-
   Get metadata for and download files produced by an Oz agent run using the
   `oz artifact` subcommands.