refactor(auth): dedup cell login refresh + tidy jurisdiction test per cleanup review

• Extract refreshCellLoginJWT, shared by resolveActiveContextCellSubject and resolveStoredCellSubject (was a duplicated ~12-line build-provider → call → map-ErrNotLoggedIn block).
• Use the existing writeActiveContext test helper for the single-context TestJurisdictionToken_StoredContext seed.
• Drop the orphaned/stale doc-comment block left stacked above TestJurisdictionToken_StoredContext.

Behavior unchanged; fmt + lint clean, tests green.