feat: side panel shows per-juror baseline and balanced contribution

Extends the ranking router's roundEvaluationScores response with
per-juror grading stats (mean, stddev, count) plus the round's overall
mean/stddev. The side-sheet juror rows render 'typical X.XX →
contributes Y.YY' next to each Score badge whenever balanced is on,
making the z-rescaling visible per individual rather than only as a
project-level number.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/server/routers/ranking.ts

@@ -537,6 +537,19 @@ export const rankingRouter = router({
         }
       }
 
-      return { byProject, balanced }
+      // Per-juror grading stats so the side panel can render each juror's
+      // personal baseline and rescaled contribution.
+      const jurorStats: Record<string, { mean: number; stddev: number; count: number }> = {}
+      for (const [userId, s] of balanceCtx.jurorStats.entries()) {
+        jurorStats[userId] = { mean: s.mean, stddev: s.stddev, count: s.count }
+      }
+
+      return {
+        byProject,
+        balanced,
+        jurorStats,
+        overallMean: balanceCtx.overallMean,
+        overallStddev: balanceCtx.overallStddev,
+      }
     }),
 })