feat(showcase): add temporary language switcher for visitors with cookie persistence

app/templates/showcase.html

@@ -2,6 +2,16 @@
 {% block title %}{{ profile_user.username }} {{ 'showcase.title'|t(lang) }}{% endblock %}
 {% block nav %}{% endblock %}
 {% block content %}
+<div class="showcase-lang-bar">
+    <div class="lang-switcher" id="langSwitcher">
+        <button type="button" class="lang-globe" onclick="document.getElementById('langDropdown').classList.toggle('show')">🌐</button>
+        <div class="lang-dropdown" id="langDropdown">
+            {% for code, name in available_languages.items() %}
+            <a href="?lang={{ code }}" class="lang-option {% if lang == code %}active{% endif %}">{{ name }}</a>
+            {% endfor %}
+        </div>
+    </div>
+</div>
 <div class="section-header">
     <h1>📮 {{ profile_user.username }} {{ 'showcase.title'|t(lang) }}</h1>
 </div>
@@ -184,5 +194,13 @@ document.addEventListener('keydown', function(e) {
     else if (e.key === 'ArrowLeft') navLightbox(-1);
     else if (e.key === 'ArrowRight') navLightbox(1);
 });
+// Close language dropdown when clicking outside
+document.addEventListener('click', function(e) {
+    var sw = document.getElementById('langSwitcher');
+    var dd = document.getElementById('langDropdown');
+    if (sw && dd && !sw.contains(e.target)) {
+        dd.classList.remove('show');
+    }
+});
 </script>
 {% endblock %}