rust(fix): return artifact app links from the artifact tools

[bill-sift]

Other MCP tools return a convenient url field to make it easier for users to follow up in the app. Updated the various artifact tools to also return a url, with the version ID when relevant.

• list_artifacts has a url since it's a standard list endpoint
• list_artifact_versions has one top level artifact_url to avoid duplicated data, which matches list_rule_versions
• download_artifact, create_artifact, update_artifact, archive_artifact, and unarchived_artifact return an artifact_url field
• Fixed escaping brackets in url rendering for all tools, since that would break markdown links
• Updated agent guidance to return markdown links instead of raw URLs

[alexa-sift]

Two small nits/nice to have:

• That tests provide mostly full coverage, but would be nice to have a screenshot of an agent showing the proper artifcat url link now
• Do we need to worry about a display name containing a stray ], like results v2].csv, breaking the link?

[bill-sift]

• We need to merge the PR first to pick up the new version of the MCP for manual testing, so that will come later
• Good catch! Fixed in the shared helper so it will apply to all callers