feat: 导航开关与 CTP 柜台手续费

系统设置可开关五类导航；手续费默认从 CTP 查询同步，本地/AKShare 作离线兜底；补充 FEES.md。

Co-authored-by: Cursor <cursoragent@cursor.com>

templates/settings.html

@@ -2,6 +2,23 @@
 {% block title %}系统设置 - 国内期货监控系统{% endblock %}
 {% block content %}
 
+<div class="card">
+    <h2>导航显示</h2>
+    <form action="{{ url_for('settings') }}" method="post">
+        <input type="hidden" name="action" value="nav">
+        <p class="hint" style="margin-bottom:.75rem">关闭后顶栏隐藏对应入口，直接访问 URL 也会跳转回持仓监控。</p>
+        <div class="form-grid" style="max-width:640px;grid-template-columns:1fr 1fr">
+            {% for key, label in nav_toggles.items() %}
+            <label class="field" style="display:flex;align-items:center;gap:.5rem;cursor:pointer">
+                <input type="checkbox" name="nav_{{ key }}" {% if nav_items[key] %}checked{% endif %}>
+                <span>{{ label }}</span>
+            </label>
+            {% endfor %}
+        </div>
+        <button type="submit" class="btn-primary" style="margin-top:.75rem">保存导航</button>
+    </form>
+</div>
+
 <div class="card">
     <h2>交易模式</h2>
     <form action="{{ url_for('settings') }}" method="post">