visual redesign: landing, dashboard overview, session calendar (2.3.1)

- Redesign landing page hero with split layout, features section, and in-app session/result demos
- Add fixed sidebar scroll isolation (app-shell overflow lock pattern)
- Redesign leagues index cards with initial badge, podium leader chips, and action links
- Redesign league dashboard: color-coded nav tiles, cash/stats overview strip, session history heatmap calendar
- Dashboard cash stats use real cash only (excludes rollovers and carry-ins)
- Session history calendar: JS-driven full-year grid, year navigation, hover tooltips, full-width responsive layout
- Bump leaderboard tile color from gold to blue (distinct from ledger orange)
- Bump version to 2.3.1

templates/account_settings.html

@@ -2,14 +2,13 @@
 {% block title %}Account settings · myboker.org{% endblock %}
 {% block content %}
 
-<div class="hero" style="padding-bottom:18px;">
-    <p class="hero__kicker">Account</p>
-    <h1 class="hero__title">Settings</h1>
-    <p class="hero__sub">Manage your email address, password, and account.</p>
-</div>
-
-<div class="toolbar">
-    <div class="toolbar__left">
+<div class="settings-profile">
+    <div class="settings-avatar">{{ user.email[0] | upper }}</div>
+    <div class="settings-profile__meta">
+        <h1 class="settings-profile__title">Account Settings</h1>
+        <p class="settings-profile__email">{{ user.email }}</p>
+    </div>
+    <div style="margin-left:auto;">
         <a class="btn btn--ghost btn--sm" href="{{ url_for('leagues.index') }}">My leagues</a>
     </div>
 </div>