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/dashboard/edit.html

@@ -1,5 +1,5 @@
 {% extends "base.html" %}
-{% block title %}Edit: {{ dashboard.name }} — Fabled Scryer{% endblock %}
+{% block title %}Edit: {{ dashboard.name }} — Roundtable{% endblock %}
 {% block content %}
 <div style="display:flex;align-items:baseline;justify-content:space-between;margin-bottom:1.5rem;">
   <h1 class="page-title" style="margin-bottom:0;">Edit: {{ dashboard.name }}</h1>