🐛 Contributor-lane auto-merge ignores the operator-set registry tier; trusted contributors skip with no-linked-issue / no-claim #12166

Summary

The automerge contributor lane (src/pkg/github/automerge/automerge_contributor_lane.go, introduced by #12051) only merges a non-App-authored PR when the PR closes an issue (closing keyword) whose App-authored hive:claim marker says kind=contributor who=<author> hive=<this hive> tier=<require_tiers> verified=true. The tier is read only from the claim marker; the operator-set trust tier in the hive's contributor registry (Contribute → Admin → trust tier) is never consulted.

So an operator marking a contributor trusted has no effect on auto-merge unless every PR that contributor opens closes a relay-claimed issue.

Observed on hive's own hive

Contributor mrbobbytables is trusted in the contributor registry, yet the sweep skipped:

• 🐛 Stop task-list sweep hard-parking issues on prose needs-human #12045 — body Part of #12002 (a reference, not a closing keyword) → automerge skip … reason=contributor-lane:no-linked-issue tier=contributor-lane
• 🐛 hub: wait out resolver timeout in SHA test helpers #11756 — issue was claimed outside the relay (no App-authored hive:claim marker) → automerge skip … reason=contributor-lane:no-claim tier=contributor-lane

Both PRs were CI-green and reviewer-approved; both waited for a manual /lgtm the maintainer did not want to give ("if I have them trusted I don't want to be bothered").

Expected

If the PR author is present in the contributor registry with a tier in auto_merge.contributor_lane.require_tiers (default trusted, merger), the lane should treat the claim/tier requirement as satisfied without a linked issue or hive:claim marker. All other gates stay (author_association, workflow/test diff fences, CI green, reviewer verdict, soak, labels, human-merge paths). The admit path should be logged distinctly (e.g. contributor-lane:registry-trusted) so operators can tell a registry-admitted merge from a marker-admitted one, and the existing marker path should stay intact for contributors not in the registry.

Config-gate it following the existing auto_merge.contributor_lane.* pattern (registry_tiers_sufficient, default true).

Refs #12051.