feat: add a reviewer queue for pending Socials actions

[chubes4]

Dependency

Blocked by #40. The queue must read Data Machine pending actions, not legacy Studio posts.

Investigation requirement

First inspect Data Machine’s current pending-actions admin, abilities, and REST surfaces. Build a Studio-specific screen only for the UX that the generic owner-layer surface cannot provide.

Goal

Give authorized Socials reviewers a focused queue showing:

• requester and submitted time
• target platform/account
• caption and media preview
• action state and prior resolution attempts
• approve/reject controls
• publish result or actionable failure

Acceptance criteria

• Access requires the existing Socials reviewer capability, not generic team membership alone.
• Queue data comes from PendingActionStore through its canonical read contract.
• Resolve actions are idempotent and re-check permissions.
• The screen links to receipt/error evidence after resolution.
• No duplicate pending-action table or REST route is introduced.
• Empty, loading, failed, approved, and rejected states are covered.