Envelope budget: Budget page, per-month assignments stored on a Budget tab, rollover and ready-to-assign

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

app_dashboard.html

@@ -30,7 +30,7 @@ td.n,th.n{text-align:right;font-variant-numeric:tabular-nums}.scroll{max-height:
 <body>
 <main>
   <div class="row"><h1>Bills Dashboard</h1><span class="mute" id="updated"></span><div class="spacer"></div>
-    <label class="mute">Year <select id="year"></select></label><a href="/">← Statement Loader</a></div>
+    <label class="mute">Year <select id="year"></select></label><a href="/budget">Budget</a><a href="/">← Statement Loader</a></div>
   <div class="kpis" id="kpis"></div>
   <div class="grid">
     <div class="card"><h2 id="t0">Income vs spending</h2><div id="c0"></div><div class="legend" id="l0"></div></div>