GitHub credential picker shows unknown for designated

Found while working Task 9178. On app.jaah.ai as Debug Admin acting in the Operator org, Settings › Integrations › GitHub shows "Unknown credential" for both **GitHub App credential** and **OAuth App credential**, though both are designated (`gmind/system/github-app`, `gmind/system/github-oauth`, both in org zero) and `/api/settings` returns their ids. The page's `GET /api/credentials/<id>` lookups answer 404, so the picker cannot name them and the operator cannot tell what is configured. - Make the setting's credential picker name a designated operator-plane credential, whichever operator org the viewer is acting in. - If the row really is unreadable to the viewer, say why (e.g. "In another org") instead of "Unknown credential". Out of scope: changing which credentials are designated; the GitHub connect flows. Done means: on a stack with both GitHub app credentials designated in org zero, an operator acting in the Operator org sees both settings show the credential's name; a test covers the lookup.

Settings credential pickers now name org-zero credentials under any operator org filter; a 404 says "Deleted credential"/"Deleted or not shared". Quick gate + tests green, visual check done (both names shown). PR #6695 queued to the lane. Deferred: picker option list still filter-narrowed. Memory: used mem-18077; proposed 0.