Add balance monitor, low-balance admin banner, dry-run auto-topup (sweep) framework

templates/admin.html

@@ -1,6 +1,11 @@
 {% extends "base.html" %}
 {% block body %}
 <h2>Admin</h2>
+{% if low_balance %}
+<div class="flash warn" style="font-size:15px;border-color:var(--danger);color:var(--danger);background:rgba(255,77,109,.08)">
+  ⚠️ IPRoyal balance LOW (${{ ipr_balance }}) — top up now or dedicated orders will fail.
+</div>
+{% endif %}
 <div class="stats-row">
   <div class="card stat"><span class="lbl">Revenue (paid)</span><span class="val">{{ stats.revenue_sats }} sats</span></div>
   <div class="card stat"><span class="lbl">IPRoyal balance</span><span class="val">${{ ipr_balance }}</span></div>