fix(navigation): keep menu icon glyphs out of the links' accessible names

Font Awesome 6 paints each icon through ::before with a private-use
character, and the menu's <i> elements carried no aria-hidden, so every
menu link's accessible name began with that glyph: the Login link was
announced as " Login". Screen readers read the glyph, and exact
name matches such as Playwright's getByRole("link", { name: /^login$/i })
never found the link, which left infinito-nexus's post-login check that
the Login control is gone passing without ever looking at it.

The icons of the navigation macro and of the language menu are now
aria-hidden, as Font Awesome recommends for decorative icons. A unit
test holds every icon of the rendered header to it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

app/templates/moduls/navigation.html.j2

@@ -1,5 +1,5 @@
 {% macro render_icon_and_name(item) %}
-    <i class="{{ item.icon.class if item.icon is defined and item.icon.class is defined else 'fa-solid fa-link' }}"></i>
+    <i class="{{ item.icon.class if item.icon is defined and item.icon.class is defined else 'fa-solid fa-link' }}" aria-hidden="true"></i>
     {% if item.name is defined %}
         {{ item.name }}
     {% else %}
@@ -101,7 +101,7 @@
             {% if menu_type == "header" %}
             <li class="nav-item dropdown">
                 <a class="nav-link dropdown-toggle btn btn-light" id="navbarDropdownLanguage" role="button" data-bs-toggle="dropdown" data-bs-display="dynamic" aria-expanded="false" title="{{ t('Language') }}">
-                    <i class="fa-solid fa-language"></i> {{ languages[lang] }}
+                    <i class="fa-solid fa-language" aria-hidden="true"></i> {{ languages[lang] }}
                 </a>
                 <ul class="dropdown-menu language-menu">
                     {% for code, endonym in languages.items() %}