SP-347: add asset-registry skills list command

[Kastriot Salihu (ksalihu)]

Summary

Adds content-cli asset-registry skills list to discover all agent skills registered in the asset registry (name, description, path), backed by GET /pacman/api/core/asset-registry/skills.

Linked

https://celonis.atlassian.net/browse/SP-347

What changed

• Introduced an asset-registry skills sub-command group so follow-up skill commands (get, file download, etc.) can slot in under the same tree.
• asset-registry skills list — prints one line per skill: () - (description omitted when empty); logs No agent skills registered. when the list is empty.
• asset-registry skills list --json — writes the full API response to a UUID-named JSON file in the working directory (same pattern as asset-registry list --json).
• Types: AgentSkill, AgentSkillMetadata, AgentSkillsResponse.
• User guide: new List Skills section in docs/user-guide/asset-registry-commands.md.

Test plan

• content-cli asset-registry skills list --profile — verify non-empty output against develop realm
• content-cli asset-registry skills list --profile --json — verify file is written and contains skills[] with name, description, path, metadata.version

[sonarqubecloud]

Quality Gate failed

Failed conditions
68.8% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud