test(settings): coverage-save snapshot tests miss two mutants #551

Summary

The settings coverage-save tests added in #538 leave mutants alive, and one branch is dead code.

Location (origin/main 5659f3b)

• frontend/src/settings.ts saveGlobalSettings (~3525-3625). Reported in review as surviving the suite: (a) the card snapshot (savedSnapshot[field.coverageId], ~3619) updated even when the service PUT fails; (b) the global snapshot (savedSnapshot['setting-default-coverage'], ~3538) refreshed before the global PUT resolves. Neither mutation fails a test. (Not re-run for this issue; the mutations come from the review.)
• Dead ternary at ~3560: defaultCoverageChanged ? settings.default_coverage : (base?.coverage ?? settings.default_coverage). After the global PUT, loadedServiceConfigs is already remapped to settings.default_coverage (~3539), so base?.coverage equals it whenever defaultCoverageChanged is true and the ternary adds nothing.

Not filed here

Empty global coverage still passing 0 in frontend/src/plans.ts:1345 and no inline error from wireInlineRangeValidation (settings.ts:247) are already described in open #522.

Context

Found in the #538 review. Related: #522, #539.

Acceptance

Tests fail when the card snapshot is updated after a failed service PUT and when the global snapshot is refreshed before its PUT resolves, and the redundant ternary is removed.