feat: add 10 UX improvements from interface review

- Stale data banner after 3 consecutive fetch failures, auto-clears on recovery
- Date navigation with left/right arrows (Yesterday/Today/Tomorrow labels),
  fetches from NHL API for non-today dates, disables auto-refresh on history
- Empty state message when no games are scheduled
- Series detail page auto-refreshes every 30s when a game is live
- Notification permission deferred until a playoff OT actually occurs
- Scroll position saved/restored when navigating to/from series detail
- Team records rendered with better contrast and tabular nums
- Active bracket round highlighted with gold heading + underline,
  completed rounds dimmed more aggressively, mobile accordion auto-opens
  current round
- Browser tab title shows live game count (e.g. "NHL Scoreboard (3 Live)")
- Service worker update shows a dismissable toast instead of force-reloading

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/series_view.py

@@ -77,6 +77,7 @@ def build_series_view(series_id, payload):
         "played_games": played,
         "next_game": next_game,
         "series_logo": payload.get("seriesLogo"),
+        "has_live": any(g["live"] for g in normalized_games),
     }