feat: make scoreboard playoff-aware with banner, bracket, and series drill-down

Turn a regular-season-looking Tuesday into a full playoff experience:

- Playoff banner with round + day + series + elimination counts, gold/silver
  Cup theme toggled by body.playoff-mode
- Series context on each playoff card: round chip, series score, stake badges
  (GAME 7, CLINCHER, PIVOTAL), and one-line blurb
- Game 7s pin to a new Spotlight section above Live
- Playoff OT renders with SUDDEN DEATH badge and pulsing gold border
- Client-side OT notifications via bell button in the banner
- New /series/<id> drill-down with headline, next-game, and game-by-game history
- New /bracket page: 7-column desktop grid, accordion on mobile
- Day N banner count auto-anchors on first playoff scoreboard hit
- SQLite cache for bracket + per-series schedules, stale-on-failure up to 24h

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

app/templates/_bracket_matchup.html

@@ -0,0 +1,21 @@
+{% if m.empty %}
+<div class="bracket-matchup bracket-matchup-empty">
+    <div class="bracket-team bracket-team-placeholder">TBD</div>
+    <div class="bracket-team bracket-team-placeholder">TBD</div>
+</div>
+{% else %}
+<a class="bracket-matchup bracket-matchup-{{ m.state }}" href="/series/{{ m.series_id }}">
+    <div class="bracket-team {% if m.winner_abbrev == m.top.abbrev %}bracket-team-winner{% endif %}">
+        {% if m.top.logo %}<img class="bracket-team-logo" src="{{ m.top.logo }}" alt="{{ m.top.abbrev }}">{% endif %}
+        <span class="bracket-team-abbrev">{{ m.top.abbrev }}</span>
+        {% if m.top.seed %}<span class="bracket-team-seed">{{ m.top.seed }}</span>{% endif %}
+        <span class="bracket-team-wins">{{ m.top_wins }}</span>
+    </div>
+    <div class="bracket-team {% if m.winner_abbrev == m.bottom.abbrev %}bracket-team-winner{% endif %}">
+        {% if m.bottom.logo %}<img class="bracket-team-logo" src="{{ m.bottom.logo }}" alt="{{ m.bottom.abbrev }}">{% endif %}
+        <span class="bracket-team-abbrev">{{ m.bottom.abbrev }}</span>
+        {% if m.bottom.seed %}<span class="bracket-team-seed">{{ m.bottom.seed }}</span>{% endif %}
+        <span class="bracket-team-wins">{{ m.bottom_wins }}</span>
+    </div>
+</a>
+{% endif %}