add file preview

Reviewed-on: sites/file-explorer#6

templates/file.html.twig

@@ -0,0 +1,21 @@
+{% extends 'base.html.twig' %}
+
+{% block title %}
+    {{ file.name }}
+{% endblock %}
+
+{% block body %}
+    <div class="max-w-2xl mx-auto my-8 p-6 bg-white shadow-lg rounded-lg border">
+        <a href="{{ routing_service.goBack(app.request) }}" class="inline-flex items-center text-blue-600 hover:text-blue-800 font-medium transition-colors">
+            <svg xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24" stroke-width="2"
+                 stroke="currentColor" class="w-5 h-5 mr-2">
+                <path stroke-linecap="round" stroke-linejoin="round" d="M15 19l-7-7 7-7"/>
+            </svg>
+            Back
+        </a>
+
+        <div class="mt-6 text-gray-700 overflow-auto max-h-96">
+            <p class="whitespace-pre-wrap leading-relaxed break-all text-balance">{{ file.content|raw }}</p>
+        </div>
+    </div>
+{% endblock %}