fix: anchor Day N to each round's first game instead of lazy first sighting

The banner read "Day 1 of ~60" on day 2 of the playoffs because the old
anchor recorded whatever date we first polled a playoff game as Day 1.
Now round start dates come from /v1/schedule/playoff-series, so Day N
is authoritative and resets at each round boundary. Drops the noisy
"of ~60" denominator.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/static/script.js

@@ -58,8 +58,7 @@ function applyMeta(meta) {
 
     const dayEl = banner.querySelector('.meta-day');
     if (meta.day_n != null) {
-        const total = meta.day_total ? ` of ~${meta.day_total}` : '';
-        setText(dayEl, `Day ${meta.day_n}${total}`);
+        setText(dayEl, `Day ${meta.day_n}`);
         dayEl.classList.remove('hidden');
     } else {
         dayEl.classList.add('hidden');