repository set-up: the team-review prompt — an inbound endpoint for managers and the "any linked member of the team may decide" rule

[teemow]

Parent

Epic: giantswarm/giantswarm#37726 — repository set-up as a company-wide automation.
Plan: repository-setup — PRD.md (proposed in giantswarm/bumblebee-plans#56, in review; the link moves to main once merged). Slice 16 of 23.

What to build

A team, in its Slack channel, receives the asks that need its decision — a deprecation, an archive, a repository another team hands over — with an Approve button; a linked member's click is the GitHub review, submitted as that member. Swarmgeist's HITL surface (docs/slack-hitl-surface.md) decides prompts by a thread's initiator or a granted collaborator today, and the gateway has no inbound API for a third party to post a prompt (docs/api.md: the chat front door, the web adapter, admin endpoints). Both are new here.

• A new prompt kind — the team review: posted into a named channel, the change spelled out (what, which repository, the giving and the receiving team for a transfer, the PR link), an Approve button and a link to the PR for anything else. A second variant is notice-only (a completion message; the giving team's notice) and has no buttons.
• An inbound endpoint for managers to post a prompt or a notice to a channel, authenticated as a service identity (no personal token, no shared secret in a configuration file), with the team name, the channel, the text and the tool call to make on approval.
• The decision rule for this kind: any linked (musterlink) member of the named GitHub team may decide — there is no initiator; the click calls the named manager tool (giantswarm-repo-manager's approve_change) as the clicking member, passing that member's identity; a second click is refused and the message shows the outcome and who decided.

Acceptance criteria

• Unit tests: only a linked member of the named team may decide; the click invokes the tool as that member; a second click is refused; an unauthenticated post is refused; a notice renders without buttons
• Lab proof with a fixture team and channel: a manager posts an ask, a linked member approves, the tool is called with that member's identity
• docs/api.md and docs/slack-hitl-surface.md describe the endpoint, the prompt kind and the rule

Blocked by

Nothing. giantswarm-repo-manager (slice 12) wires its lifecycle asks and completion messages to this endpoint.