第一期骨架：登录、实例登记、多机总览、内嵌/新标签打开。

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

templates/dashboard.html

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+{% extends "base.html" %}
+{% block title %}总览 · 期权中控{% endblock %}
+{% block body %}
+<section class="page-head">
+  <h1>多机持仓总览</h1>
+  <button type="button" class="btn" id="btn-refresh">刷新</button>
+</section>
+<p class="muted" id="overview-status">加载中…</p>
+<div id="overview-grid" class="card-grid"></div>
+{% endblock %}
+{% block scripts %}
+<script src="{{ url_for('static', filename='hub.js') }}"></script>
+<script>HubOverview.boot();</script>
+{% endblock %}