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/bracket_view.py

@@ -42,10 +42,23 @@ def build_bracket_view(year, bracket_payload, fetched_at=None):
     west_cf = [slot(ltr) for ltr in WEST_CF]
     cup = [slot(ltr) for ltr in CUP_FINAL]
 
+    all_rounds = [
+        (1, east_r1 + west_r1),
+        (2, east_r2 + west_r2),
+        (3, east_cf + west_cf),
+        (4, cup),
+    ]
+    current_round = None
+    for r, matchups in all_rounds:
+        if any(m["state"] == "active" for m in matchups):
+            current_round = r
+            break
+
     return {
         "year": year,
         "fetched_at": fetched_at,
         "bracket_logo": (bracket_payload or {}).get("bracketLogo"),
+        "current_round": current_round,
         "east_r1": east_r1,
         "west_r1": west_r1,
         "east_r2": east_r2,
@@ -54,10 +67,10 @@ def build_bracket_view(year, bracket_payload, fetched_at=None):
         "west_cf": west_cf,
         "cup": cup,
         "rounds": [
-            {"label": ROUND_LABELS[1], "east": east_r1, "west": west_r1},
-            {"label": ROUND_LABELS[2], "east": east_r2, "west": west_r2},
-            {"label": ROUND_LABELS[3], "east": east_cf, "west": west_cf},
-            {"label": ROUND_LABELS[4], "cup": cup},
+            {"label": ROUND_LABELS[1], "round_num": 1, "east": east_r1, "west": west_r1},
+            {"label": ROUND_LABELS[2], "round_num": 2, "east": east_r2, "west": west_r2},
+            {"label": ROUND_LABELS[3], "round_num": 3, "east": east_cf, "west": west_cf},
+            {"label": ROUND_LABELS[4], "round_num": 4, "cup": cup},
         ],
     }