Add banner advertising Solid Symposium and Solid Hackathon (#951)

* Initial plan

* Add banner advertising Solid26, Solid Symposium and Solid Hackathon

Co-authored-by: jeswr <63333554+jeswr@users.noreply.github.com>
Agent-Logs-Url: https://github.com/solid/solidproject.org/sessions/d2a8934d-61ee-4fc7-b8fa-2b4b43fd5a0c

* Update banner text: Solid26 as new standard release, add symposium and hackathon links

Co-authored-by: jeswr <63333554+jeswr@users.noreply.github.com>
Agent-Logs-Url: https://github.com/solid/solidproject.org/sessions/8b4efea0-7fad-4a3c-bc90-e59053d6bc9a

* Revert unintended Gemfile.lock changes

Co-authored-by: jeswr <63333554+jeswr@users.noreply.github.com>
Agent-Logs-Url: https://github.com/solid/solidproject.org/sessions/8b4efea0-7fad-4a3c-bc90-e59053d6bc9a

* Update _layouts/default.html

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update assets/css/banner.css

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Move Liquid breadcrumbs conditional to its own line for readability

Co-authored-by: jeswr <63333554+jeswr@users.noreply.github.com>
Agent-Logs-Url: https://github.com/solid/solidproject.org/sessions/efb97971-4519-4801-a115-f81fc719f5f7

* Update hackathon link to ODI announcement page

Co-authored-by: jeswr <63333554+jeswr@users.noreply.github.com>
Agent-Logs-Url: https://github.com/solid/solidproject.org/sessions/7573e3d2-6d96-45e8-8be0-15f3809ce74f

* Remove Solid26 references from banner; announce only Symposium and Hackathon

Co-authored-by: jeswr <63333554+jeswr@users.noreply.github.com>
Agent-Logs-Url: https://github.com/solid/solidproject.org/sessions/5a8ac00f-833b-415f-827c-096d064cf0ed

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: jeswr <63333554+jeswr@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: 3 people

_layouts/default.html

@@ -34,7 +34,11 @@
         <span></span>
         <span></span>
       </button>
-    </header>{% if page.breadcrumbs %}
+    </header>
+    <div class="event-banner" role="region" aria-label="Event announcement">
+      <span aria-hidden="true">📣</span> <a href="https://sosy2026.eu/">Solid Symposium</a> (Apr 30 – May 1) · <a href="https://theodi.org/news-and-events/news/announcing-the-solid-symposium-2026/">Solid Hackathon</a> (Apr 27 – 29) · London, 2026
+    </div>
+    {% if page.breadcrumbs %}
     <nav class="breadcrumb" aria-label="breadcrumbs">
       <ol>
         <li><a href="/">Home</a></li>

assets/css/banner.css

@@ -0,0 +1,20 @@
+/* Event Banner */
+.event-banner {
+    background-color: #7C4DFF;
+    color: #fff;
+    text-align: center;
+    padding: 0.6rem 1rem;
+    font-size: 1rem;
+    line-height: 1.4;
+}
+
+.event-banner a {
+    color: #fff;
+    text-decoration: underline;
+    font-weight: bold;
+}
+
+.event-banner a:hover,
+.event-banner a:focus {
+    color: #fff;
+}

assets/css/styles.css

@@ -1,4 +1,4 @@
 ---
 permalink: /assets/styles.css
 ---
-{% capture css %}{% include_relative base.css %}{% include_relative header.css %}{% include_relative footer.css %}{% include_relative breadcrumb.css %}{% include_relative homepage.css %}{% include_relative apps.css %}{% endcapture %}{{ css | strip_newlines | replace: '   ', ' ' | replace: '  ', ' ' }}
+{% capture css %}{% include_relative base.css %}{% include_relative header.css %}{% include_relative banner.css %}{% include_relative footer.css %}{% include_relative breadcrumb.css %}{% include_relative homepage.css %}{% include_relative apps.css %}{% endcapture %}{{ css | strip_newlines | replace: '   ', ' ' | replace: '  ', ' ' }}