fix: _header page_icon rendered word → SVG icon

_header.html L54: {{ page_icon }} affichait le mot 'home'/'file'/'paperclip'
au lieu de l'icône SVG. Maintenant détecte les noms connus → fd_icon().
Fallback pour les valeurs non-reconnues: affiche tel quel.
143 tests passent

app/templates/_header.html

@@ -51,7 +51,7 @@
   <div class="topbar-left header-breadcrumb" x-data="fdBreadcrumb()" x-init="init()"
        @mouseleave="dragCloseTimer()">
     {% if page_icon %}
-    <span class="header-page-icon">{{ page_icon }}</span>
+    <span class="header-page-icon">{% if page_icon in ("folder","file","star","link","trash","book","home","settings","lock","globe","image","edit","calendar","users","user","search","tag","bar-chart","grid","list","align-left","zap","paperclip","key","refresh","upload") %}{{ fd_icon(page_icon,18) }}{% else %}{{ page_icon }}{% endif %}</span>
     {% endif %}
 
     <template x-for="(crumb, di) in display" :key="di">