Accounts tab and page: savings and mortgage balances kept separate from spending and the budget

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

app_budget.html

@@ -32,7 +32,7 @@ input.amt{width:110px;text-align:right}
 </head>
 <body>
 <main>
-  <nav class="tabs"><a href="/">Statements</a><a href="/budget" class="on" aria-current="page">Budget</a><a href="/dashboard">Dashboard</a></nav>
+  <nav class="tabs"><a href="/">Statements</a><a href="/budget" class="on" aria-current="page">Budget</a><a href="/dashboard">Dashboard</a><a href="/accounts">Accounts</a></nav>
   <div class="row"><h1>Envelope Budget</h1><div class="spacer"></div></div>
   <div class="row" style="margin:14px 0 0">
     <button id="prev">‹</button><b id="mlabel" style="min-width:120px;text-align:center;font-size:16px"></b><button id="next">›</button>