feat: icône application — favicon + logo navbar

- sources/static/icon.png : copie de icon/icon_logo.png (1024×1024)
- <link rel="icon"> et <link rel="apple-touch-icon"> dans base.html
- Remplacement du SVG générique dans la navbar par l'image logo

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

sources/templates/base.html

@@ -4,6 +4,8 @@
   <meta charset="UTF-8">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <title>{% block title %}Backup Manager{% endblock %} — {{ instance_name }}</title>
+  <link rel="icon" type="image/png" href="{{ url_for('static', filename='icon.png') }}">
+  <link rel="apple-touch-icon" href="{{ url_for('static', filename='icon.png') }}">
   <script src="https://cdn.tailwindcss.com"></script>
   <style type="text/tailwindcss">
     @layer components {
@@ -27,10 +29,7 @@
   <nav class="bg-gray-900 text-white shadow-lg">
     <div class="max-w-7xl mx-auto px-6 py-3 flex items-center justify-between">
       <div class="flex items-center gap-3">
-        <svg class="w-6 h-6 text-blue-400" fill="none" stroke="currentColor" viewBox="0 0 24 24">
-          <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2"
-            d="M5 12h14M5 12l4-4m-4 4l4 4M19 12l-4-4m4 4l-4 4"/>
-        </svg>
+        <img src="{{ url_for('static', filename='icon.png') }}" alt="logo" class="w-7 h-7 rounded">
         <a href="{{ url_for('jobs.index') }}" class="text-lg font-bold tracking-tight">Backup Manager</a>
         <span class="bg-blue-600 text-xs font-medium px-2 py-0.5 rounded">{{ instance_name }}</span>
       </div>