refactor: extract formatTimeAgo to shared utils

[wdeveloper16]

Summary

• Moves the locally-defined formatTimeAgo out of MinerScoreCard.tsx into src/utils/format.ts
• Updates the import in MinerScoreCard.tsx to use the shared utility
• Follows the same pattern as formatDate (refactor: Extract duplicated formatDate to shared utils #214) and credibilityColor (refactor: Extract duplicated credibilityColor to shared utils #215)

Net: 17 lines removed from component, 13 lines added to shared util.

Test plan

• npm run format:check — passes
• npm run lint — passes (0 warnings)
• npm run build — clean build, no TS errors
• MinerScoreCard "Updated X ago" chip still renders correctly

[wdeveloper16]

Extracts the locally-defined formatTimeAgo from MinerScoreCard.tsx into src/utils/format.ts, completing the pattern started by #214 and #215.

[wdeveloper16]

Would be it possible to review by you, @anderdc ?

[anderdc]

Closing — formatTimeAgo has a single caller. Extracting it to a shared util adds a module and an import for no reuse benefit. The abstraction cost outweighs the duplication when there's only one call site.