settings: add Exchange API tab for instance system settings.

Allow configuring perpetual API keys and live trading from Settings, reusing the existing env save API.

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

lib/instance/templates/settings_panel.html

@@ -2,7 +2,7 @@
 <div class="settings-page full">
     <div class="env-config-head card">
         <h2>系统设置</h2>
-        <p class="settings-env-hint env-config-head-hint">各区块说明见 <code>docs/系统设置说明.md</code>.</p>
+        <p class="settings-env-hint env-config-head-hint">交易所 API、账户密码、划转与显示开关等在此维护.</p>
     </div>
 
     {% if settings_tabs %}
@@ -20,6 +20,8 @@
             <section class="env-panel env-panel--{{ loop.index0 }} settings-tab-panel" role="tabpanel">
                 {% if tab.key == 'nav' %}
                     {% include 'display_prefs_panel.html' %}
+                {% elif tab.key == 'exchange_api' %}
+                    {% include 'exchange_api_settings_panel.html' %}
                 {% elif tab.key == 'password' %}
                     {% include 'password_settings_panel.html' %}
                 {% elif tab.key == 'transfer' %}