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/routes.py

@@ -8,11 +8,10 @@ from app.games import parse_games
 from app.playoff import today_meta
 from app.bracket_view import build_bracket_view
 from app.playoff_cache import (
-    day_n as compute_day_n,
+    day_n_for_round,
     fetch_series,
     get_bracket,
     parse_series_id,
-    record_start_date_if_missing,
     refresh_bracket,
 )
 from app.series_view import build_series_view
@@ -22,6 +21,17 @@ from zoneinfo import ZoneInfo
 _EASTERN = ZoneInfo("America/New_York")
 
 
+def _max_playoff_round(raw_games):
+    max_round = 0
+    for g in raw_games or []:
+        if g.get("gameType") != 3:
+            continue
+        r = (g.get("seriesStatus") or {}).get("round") or 0
+        if r > max_round:
+            max_round = r
+    return max_round or None
+
+
 @app.route("/manifest.json")
 def manifest():
     return send_from_directory(app.static_folder, "manifest.json")
@@ -61,10 +71,10 @@ def get_scoreboard():
 
     if scoreboard_data:
         raw_games = scoreboard_data.get("games", [])
-        record_start_date_if_missing(raw_games)
         games = parse_games(scoreboard_data)
-        n, total = compute_day_n()
-        meta = today_meta(raw_games, day_n=n, day_total=total)
+        max_round = _max_playoff_round(raw_games)
+        n = day_n_for_round(max_round) if max_round else None
+        meta = today_meta(raw_games, day_n=n)
 
         pinned = [g for g in games if g.get("Pinned")]
         remaining = [g for g in games if not g.get("Pinned")]