feat: optional 4-digit PIN asked in every new tab (not on reload), on-screen keypad for phones; set, change or remove it in the account; five misses sign out

internal/server/web/templates/forwards.html

@@ -5,6 +5,7 @@
 <meta name="viewport" content="width=device-width, initial-scale=1">
 <title>Порты · {{.Agent.Name}} - LPRA</title>
 <link rel="stylesheet" href="{{asset "app.css"}}">
+<script src="{{asset "pin.js"}}"></script>
 <style>
   /* One line: fixed narrow fields, the label takes what is left. */
   .frow { display:flex; align-items:flex-end; gap:12px; flex-wrap:wrap; }