#702 fix(ci): report real errors from the snapshot editor permission check

Summary

Follow-up to #698. The trusted-editor guard in Update Snapshots turned every failed collaborator-permission lookup into none, so a 403, rate limit or 5xx read as "has 'none' access". Only a 404 (no such user) now maps to none; any other failure stops with GitHub's own error. The guard still fails closed in every case.

#no-linear

Test Plan

• Ran the edited step against a stub gh for write, read, none, 404, 403, 500 and network failures, plus a fork head repo. Write passes; read, none and 404 report missing access; 403, 500 and network failures report the real error; the fork fails the same-repo check.
• shellcheck clean; actionlint shows only the existing arc runner label.
• Dispatch on this branch against a fork PR stops at the same-repo check.
• Writer acceptance on a same-repo PR not exercised here.

Docs

• No docs update needed.

🤖 Generated with Claude Code

https://claude.ai/code/session_01GziRseGZMsJ5Yf7EboZLMc

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Summary by cubic

Fixes the snapshot editor permission check in the update-snapshots workflow so 403s, rate limits, and 5xx errors now stop the job with GitHub's real error, instead of being read as "none" access. Only a 404 (no such user) maps to "none"; the guard still fails closed in every case.