Add suff drink booking tool with PIN auth

Self-service drink tab at /suff/ for festival attendees. Users log in
with username + 3-digit PIN stored in a separate User.pin field, so
staff/admin accounts can keep their strong password for /admin/ and
also use the drink tool with the same username. PINs for staff users
must be set from the admin panel via a dedicated "PIN setzen" view to
prevent account takeover by name collision.

Time-gated to the festival window (Thu–Sun in Berlin tz) with phases
before/booking/readonly/closed; in non-production mode the tool is
always in booking phase for local testing.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

gaehsnitz/templates/suff/name.html

@@ -0,0 +1,19 @@
+{% extends "suff/base.html" %}
+
+{% block content %}
+<h2>Wer bist du?</h2>
+<p>
+    Gib deinen Namen ein. Sonderzeichen, Leerzeichen und Großbuchstaben werden
+    entfernt (z.B. wird aus "Flo Hä!" → "flo-ha"). Merk dir den Namen so,
+    wie er hier nach dem Anlegen angezeigt wird.
+</p>
+{% if error %}<p><b>{{ error }}</b></p>{% endif %}
+<form method="post" action="{% url 'suff:name' %}">
+    {% csrf_token %}
+    <label>
+        Name:
+        <input type="text" name="name" autofocus required />
+    </label>
+    <button type="submit">Weiter</button>
+</form>
+{% endblock %}