copy: flip visible wordmark → Roundtable

Updates nav brand, page <title> blocks across all templates, and the
read-only share view footer. Removes duplicate Roundtable heading from
login card now that the nav wordmark reads correctly.

roundtable/templates/hosts/form.html

@@ -1,5 +1,5 @@
 {% extends "base.html" %}
-{% block title %}{% if host %}Edit Host{% else %}New Host{% endif %} — Fabled Scryer{% endblock %}
+{% block title %}{% if host %}Edit Host{% else %}New Host{% endif %} — Roundtable{% endblock %}
 {% block content %}
 <div style="max-width:560px;margin:2rem auto;">
     <h1 class="page-title">{% if host %}Edit Host{% else %}Add Host{% endif %}</h1>