fix: discoveries miner card shows issue stats only

[Dexterity104]

Summary

Fixes #277. On /discoveries, miner cards mixed PR donut slices with an issue credibility percentage and stacked a second row of issue stats below the PR row. The donut and the stats row now share one segments array, so the chart segments, labels, and center percentage always describe the same data.

Changes

• Introduce getSegments(miner, variant) as the single source of truth for the three segments rendered on the card (Solved/Open/Closed for discoveries, Merged/Open/Closed for oss).
• Donut data maps over the same segments with positional chart colors and inactive ratios, so it can never diverge from the labels.
• Remove the separate IssueStatsSection (~130 lines); the footer is now a single grid row for both variants.
• Extract small StatCell and StatLabel helpers to drop the repeated Typography boilerplate.

Scope

• Discoveries page: donut + stats now issue-only, matching the percentage.
• OSS Contributions page: unchanged.

Test plan

• Visit /discoveries and confirm each card shows Solved / Open / Closed with a donut whose segments match those counts.
• Hover the donut and confirm tooltips reflect issue counts.
• Visit /leaderboard (oss) and confirm Merged / Open / Closed PR stats are unchanged.
• Check an ineligible miner card on both pages for correct dimmed styling.
• npx tsc --noEmit passes.

[Dexterity104]

[anderdc]

resolve conflicts

[Dexterity104]

@anderdc I've resolved the conflicts. Could you review it again please?

[anderdc]

very clean PR, LGTM

[Dexterity104]

Thanks a lot, @anderdc