Batch fetch results for smoother card transitions

[MathijsR94]

Summary

• Replace progressive per-user setResults calls with Promise.allSettled + a single batched state update
• Cards now stay in skeleton state until all fetches complete, then transition together with badges already computed
• Eliminates badge flickering caused by computeBadges re-running on every individual result update

Test plan

• Fetch with 2+ users — all cards should show skeleton, then appear together with badges
• Trigger a fetch error (e.g. typo in username) — errored card shows error, others show data, all in one transition
• Change date range mid-fetch — stale results should not be applied (abort guard)
• Add a single user via settings — still updates progressively (uses fetchUser, not fetchAll)