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/routes.py

@@ -1,6 +1,8 @@
 import json
+import logging
 
-from flask import abort, make_response, render_template, jsonify, send_from_directory
+import requests as http_requests
+from flask import abort, make_response, render_template, jsonify, request, send_from_directory
 
 from app import APP_VERSION, app, static_v
 from app.config import SCOREBOARD_DATA_FILE
@@ -19,6 +21,18 @@ from datetime import datetime
 from zoneinfo import ZoneInfo
 
 _EASTERN = ZoneInfo("America/New_York")
+_logger = logging.getLogger(__name__)
+
+
+def _fetch_date(date_str):
+    url = f"https://api-web.nhle.com/v1/score/{date_str}"
+    try:
+        resp = http_requests.get(url, timeout=10)
+        resp.raise_for_status()
+        return resp.json()
+    except http_requests.RequestException as e:
+        _logger.error("Failed to fetch scores for %s: %s", date_str, e)
+        return None
 
 
 def _max_playoff_round(raw_games):
@@ -69,15 +83,27 @@ def index():
 
 @app.route("/scoreboard")
 def get_scoreboard():
-    try:
-        with open(SCOREBOARD_DATA_FILE, "r") as json_file:
-            scoreboard_data = json.load(json_file)
-    except FileNotFoundError:
-        return jsonify({"error": "Failed to retrieve scoreboard data. File not found."})
-    except json.JSONDecodeError:
-        return jsonify(
-            {"error": "Failed to retrieve scoreboard data. Invalid JSON format."}
-        )
+    date_param = request.args.get("date")
+    today_str = datetime.now(_EASTERN).strftime("%Y-%m-%d")
+
+    if date_param and date_param != today_str:
+        try:
+            datetime.strptime(date_param, "%Y-%m-%d")
+        except ValueError:
+            return jsonify({"error": "Invalid date format. Use YYYY-MM-DD."}), 400
+        scoreboard_data = _fetch_date(date_param)
+        if not scoreboard_data:
+            return jsonify({"error": "Failed to retrieve scoreboard data for that date."})
+    else:
+        try:
+            with open(SCOREBOARD_DATA_FILE, "r") as json_file:
+                scoreboard_data = json.load(json_file)
+        except FileNotFoundError:
+            return jsonify({"error": "Failed to retrieve scoreboard data. File not found."})
+        except json.JSONDecodeError:
+            return jsonify(
+                {"error": "Failed to retrieve scoreboard data. Invalid JSON format."}
+            )
 
     if scoreboard_data:
         raw_games = scoreboard_data.get("games", [])