ui: replace text header with logo.svg, add copyright footer

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

templates/base.html

@@ -12,9 +12,8 @@
 <body>
     <div class="d-flex">
         <nav class="sidebar bg-dark text-white d-flex flex-column">
-            <div class="p-3 border-bottom border-secondary">
-                <h5 class="mb-0"><i class="bi bi-lightbulb-fill text-warning"></i> Busylight</h5>
-                <small class="text-secondary">cynfo GmbH</small>
+            <div class="p-3 border-bottom border-secondary text-center">
+                <a href="/"><img src="/static/logo.svg" alt="cynfo" style="height: 32px; filter: brightness(0) invert(1);"></a>
             </div>
             <ul class="nav flex-column mt-2 flex-grow-1">
                 <li class="nav-item">
@@ -73,6 +72,9 @@
                         <a href="/login" class="text-light small"><i class="bi bi-box-arrow-in-right"></i> Anmelden</a>
                     {% endif %}
                 </div>
+                <div class="mt-2">
+                    <small class="text-secondary" style="font-size:0.65rem">&copy; cynfo GmbH</small>
+                </div>
             </div>
         </nav>