feat: add groomer task mode

[joryirving]

Parent: #392

Add a generic groomer task mode for issue management work.

Groomer responsibilities:

• enrich unclear issues
• assign status
• assign lane
• close completed issues
• surface work that needs human input

Groomer non-goals:

• implementation work
• opening PRs
• normal worker pickup

Acceptance:

• groomer gets one grooming task at a time
• untriaged/no-status issues can appear here
• backlog issues can be promoted when ready
• finished work can be closed out
• worker queues remain separate from groomer work