Revert clickable title to Furo default and add ecosystem link under it

src/qiskit_sphinx_theme/assets/styles/_left-sidebar.scss

@@ -48,6 +48,20 @@ body {
 .sidebar-logo {
   width: 100%;
 }
+.sidebar-ecosystem-link {
+  padding-left: var(--sidebar-item-spacing-horizontal);
+  font-size: var(--sidebar-caption-font-size);
+
+  // Based off of `.sidebar-tree .reference`. Just taking the external link logo.
+  .reference {
+    // Add a nice little "external-link" arrow here.
+    &.external::after {
+      content: url('data:image/svg+xml,<svg width="12" height="12" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" stroke-width="1.5" stroke="%23607D8B" fill="none" stroke-linecap="round" stroke-linejoin="round"><path stroke="none" d="M0 0h24v24H0z"/><path d="M11 7h-5a2 2 0 0 0 -2 2v9a2 2 0 0 0 2 2h9a2 2 0 0 0 2 -2v-5" /><line x1="10" y1="14" x2="20" y2="4" /><polyline points="15 4 20 4 20 9" /></svg>');
+      margin: 0 0.25rem;
+      vertical-align: middle;
+    }
+  }
+}
 
 // --------------------------------------------------------------------------------------
 // Common config for Translations & Previous Releases

src/qiskit_sphinx_theme/theme/qiskit-sphinx-theme/custom_templates/sidebar_brand.html

@@ -2,22 +2,7 @@
   This file is inspired by Furo (created by Pradyun Gedam) and used under the MIT license.
 -#}
 
-
-{#- We default to showing a Qiskit Ecosystem logo -#}
-{%- if not logo_url and not theme_light_logo and not theme_dark_logo and not theme_disable_ecosystem_logo -%}
-<div class="sidebar-brand">
-  <a href="https://qiskit.github.io/ecosystem/">
-    <div class="sidebar-logo-container">
-      <img class="sidebar-logo" src="{{ pathto('_static/images/ecosystem-logo.svg', 1) }}" alt="Qiskit Ecosystem logo"/>
-    </div>
-  </a>
-  {% if not theme_sidebar_hide_name %}
-  <span class="sidebar-brand-text">{{ docstitle if docstitle else project }}</span>
-  {%- endif %}
-</div>
-
-{#- Else, use Furo's sidebar code. But, we remove the `centered` class from the `a` element because Carbon left-aligns things. -#}
-{%- else %}
+{#- Use Furo's sidebar code. But, we remove the `centered` class from the `a` element because Carbon left-aligns things. -#}
 <a class="sidebar-brand" href="{{ pathto(master_doc) }}">
   {% block brand_content %}
   {%- if logo_url %}
@@ -36,4 +21,7 @@
   {%- endif %}
   {% endblock brand_content %}
 </a>
-{%- endif %}
+{#- Add a link to the Qiskit ecosystem web page. -#}
+<p class="sidebar-ecosystem-link">
+  This project is part of the <a class="reference external" href="https://qiskit.github.io/ecosystem/">Qiskit ecosystem</a>
+</p>