Elo trajectories: a century of strength on every team page

buildRatings samples each WC team's rating along the full walk (yearly
historically, monthly since 2022) into elohistory.json (~72KB, 48
teams). Team pages plot it as a clean SVG line with year and rating
gridlines — Germany's century, 1908 → today, in one glance.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scripts/buildRatings.ts

@@ -74,6 +74,19 @@ function main(): void {
   let sxy = 0, sxx = 0; // regression of goal-diff on effective Elo diff
   const calib: { d: number; h: number; a: number }[] = [];
 
+  // Per-WC-team Elo trajectories: one sample per year historically, one per
+  // month for the recent window — small enough to serve, rich enough to plot.
+  const wcSet = new Set(ALL_TEAMS);
+  const RECENT_FROM = '2022-01-01';
+  const history = new Map<string, Map<string, number>>(); // team → periodKey → rating
+  const sample = (team: string, date: string, rating: number): void => {
+    if (!wcSet.has(team)) return;
+    const key = date >= RECENT_FROM ? date.slice(0, 7) : date.slice(0, 4);
+    let m = history.get(team);
+    if (!m) { m = new Map(); history.set(team, m); }
+    m.set(key, Math.round(rating));
+  };
+
   let lastDate = '';
   for (const r of rows) {
     const home = canonicalTeam(r.home);
@@ -98,6 +111,8 @@ function main(): void {
     const fastDelta = eloDelta(r.hs, r.as, feh, fea, k * FAST_M, homeAdv);
     eloFast.set(home, feh + fastDelta);
     eloFast.set(away, fea - fastDelta);
+    sample(home, r.date, eh + delta);
+    sample(away, r.date, ea - delta);
     lastDate = r.date;
   }
 
@@ -202,6 +217,14 @@ function main(): void {
   mkdirSync(OUT_DIR, { recursive: true });
   writeFileSync(join(OUT_DIR, 'ratings.json'), JSON.stringify(out));
 
+  // Per-team Elo trajectories for the team pages.
+  const eloHistory: Record<string, [string, number][]> = {};
+  for (const [team, m] of history) {
+    eloHistory[team] = [...m.entries()].sort((a, b) => a[0].localeCompare(b[0]));
+  }
+  writeFileSync(join(OUT_DIR, 'elohistory.json'), JSON.stringify({ recentFrom: RECENT_FROM, teams: eloHistory }));
+  console.log(`elo history → public/data/elohistory.json (${Object.keys(eloHistory).length} teams)`);
+
   // Compact training rows for the server's nightly in-tournament Team-DC refit
   // (absolute dates, so daysAgo can be recomputed as the tournament progresses).
   const dcRows = rows