Fix blank page when switching year group

[ravisharma-09]

Follow-up to #24, which is already merged. Switching between 1st Year and 2nd Year left the page rendering nothing until the next fetch landed. On the live second-year roster that is a blank screen for as long as GitHub takes, so it looked like the page had broken.

Reproduced in development in both directions, on PR Statistics, Quality PRs and GSoC Ready.

Cause

A half-reset. Changing year cleared the fetched data but not the loading flag, so the render fell into the loading branch while loading was still false and no error was set — and the state component draws nothing in that combination.

The data was being cleared inside an effect, which React warns against for exactly this reason: every piece of state has to be remembered and reset separately, and the one that gets missed is invisible until somebody hits the gap. I introduced this in #24 while satisfying that same lint rule, which is a fair sign the pattern was the wrong one.

Fix

The subtree is now keyed on the cohort, so switching year remounts it and every value starts fresh: the numbers, the loading flag, the last error, and the author and member filters, which otherwise list people who are not in the other year group.

This is React's own answer to "reset all state when an input changes", and unlike a manual reset it cannot drift — state added later is covered without anybody remembering to reset it here.

The key is applied by a small client component inside the Suspense boundary that already existed, so the pages above it still prerender rather than the whole route turning dynamic.

Result

Switching now shows a spinner immediately and never goes blank. Sampling the DOM every 150ms across a switch, the page goes straight from one cohort's content to a spinner to the other's.

Also removes the derived-staleness workarounds the remount makes redundant, which is why three components get smaller.

Checks

• npm run build passes; all six pages still prerender statically (○).
• npx tsc --noEmit clean.
• Zero lint errors in the touched files; the 6 remaining warnings are the pre-existing <img> ones.

🤖 Generated with Claude Code

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