many styling changes to applets and palettes applet esp.; all applets seeded w. < 3rows bumped to 3 w. new migration in apps.applets; setting palette no longer reloads entire page, only preset background-color vars; two new ITs in apps.dash.tests.ITs.test_views.SetPaletteTest to ensure dash.views functionality fires; unified h2 applet title html structure & styled its text vertically to waste less applet space

src/templates/apps/dashboard/_partials/_applet-username.html

@@ -2,6 +2,7 @@
     id="id_applet_username"
     style="--applet-cols: {{ entry.applet.grid_cols }}; --applet-rows: {{ entry.applet.grid_rows }};"
 >
+    <h2>Username</h2>
     <form method="POST" action="{% url "set_profile" %}">
         {% csrf_token %}
         <div class="username-field">