Panel: German/English, redesigned sidebar, in-game admins page, Steam Web API key link, RAR/7z save upload (SharpCompress), responsive cards; upload errors return 400; tests

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Panel/index.html

@@ -6,11 +6,13 @@
   <title>MSCO Server Panel</title>
   <link rel="icon" href="logo.png">
   <link rel="stylesheet" href="app.css">
+  <script src="i18n.js" defer></script>
   <script src="app.js" defer></script>
 </head>
 <body>
   <!-- Anmeldung / Einrichtung -->
   <main id="auth" class="auth hidden">
+    <div class="auth-lang lang-switch" data-lang-switch></div>
     <form id="authForm" class="auth-card" autocomplete="on">
       <div class="brand">
         <img src="logo.png" alt="">
@@ -48,10 +50,23 @@
           <div class="brand-sub">Server Panel</div>
         </div>
       </div>
+      <div class="server-card" id="serverCard">
+        <span class="sc-dot" id="scDot"></span>
+        <div class="sc-text">
+          <b id="scName">MSCO Server</b>
+          <small id="scState">…</small>
+        </div>
+      </div>
       <nav id="nav"></nav>
       <div class="sidebar-foot">
-        <div class="me"><span id="meName"></span><span id="meRole" class="pill"></span></div>
-        <button class="btn ghost small" id="logout" type="button">Log out</button>
+        <div class="lang-switch" data-lang-switch></div>
+        <div class="me-card">
+          <button class="me-main" id="meButton" type="button" title="My Account">
+            <span class="avatar" id="meAvatar">?</span>
+            <span class="me-text"><b id="meName"></b><small id="meRole"></small></span>
+          </button>
+          <button class="icon-btn" id="logout" type="button" title="Log out" aria-label="Log out">⏻</button>
+        </div>
       </div>
     </aside>
     <section class="content">