auth: name the core in the refresh re-login hint
Commit

When a refresh fails (expired/revoked family, or no refresh token), the
error now points at the specific core — ENTIRE_AUTH_BASE_URL=<core> entire login — so a multi-core user re-authenticates against the right
one. Matches clusterdiscovery.RenderLoginHint's idiom.
Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com Entire-Checkpoint: 22da7112c436
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