feat: API-Keys-Verwaltung in DB statt appsettings

- Neue Tabelle api_keys (Provider, Name, ApiKey, IsActive)
- Admin-CRUD: GET/POST/PUT/DELETE /api/admin/api-keys
- Aktivieren/Deaktivieren pro Provider (nur einer aktiv)
- Live-Token-Update im AnthropicService ohne Neustart
- Migration: AnthropicToken aus appsettings.Production.json → DB
- AnthropicToken aus ServerSettings-Definitionen + appsettings entfernt
- Frontend: API-Keys-Seite mit Erstellen/Bearbeiten/Löschen/Toggle
- Dashboard: API-Keys-Link für Admins

wwwroot/index.html

@@ -57,6 +57,7 @@
       <div class="dashboard-links">
         <a id="dashboardSettingsLink" class="dashboard-link">Einstellungen</a>
         <a id="dashboardAdminLink" class="dashboard-link" hidden>Benutzerverwaltung</a>
+        <a id="dashboardApiKeysLink" class="dashboard-link" hidden>API-Keys</a>
         <a id="dashboardServerSettingsLink" class="dashboard-link" hidden>Servereinstellungen</a>
         <a id="dashboardProfileLink" class="dashboard-link">Mein Profil</a>
       </div>
@@ -539,6 +540,39 @@
   </div>
 </template>
 
+<template id="tpl-api-keys">
+  <div class="page form-page">
+    <header>
+      <button class="back-btn icon-btn" data-page="dashboard"><i class="fa fa-arrow-left"></i></button>
+      <h1>API-Keys</h1>
+    </header>
+    <div class="page-content">
+      <div class="form">
+        <div class="section-header">
+          <h2>API-Key</h2>
+          <button id="apiKeysNewBtn" class="section-add-btn"><i class="fa fa-plus"></i> Neuer Key</button>
+        </div>
+        <div id="apiKeysList" class="admin-user-list"></div>
+      </div>
+
+      <div id="apiKeysForm" class="form" hidden>
+        <h2 id="apiKeysFormTitle">Neuer API-Key</h2>
+        <label>Provider</label>
+        <select id="apiKeysProvider">
+          <option value="anthropic">Anthropic</option>
+        </select>
+        <label>Name</label>
+        <input type="text" id="apiKeysName" placeholder="z.B. Mein Pro Key" autocomplete="off">
+        <label>API-Key</label>
+        <input type="text" id="apiKeysKey" placeholder="sk-ant-..." autocomplete="off">
+        <div class="form-actions">
+          <button id="apiKeysFormSaveBtn">Erstellen</button>
+        </div>
+      </div>
+    </div>
+  </div>
+</template>
+
 <template id="tpl-admin">
   <div class="page form-page">
     <header>
@@ -642,6 +676,7 @@
 <script src="js/pages/settings-page.js"></script>
 <script src="js/pages/profile-page.js"></script>
 <script src="js/pages/admin-page.js"></script>
+<script src="js/pages/api-keys-page.js"></script>
 <script src="js/pages/server-settings-page.js"></script>
 <script src="js/pages/shared-page.js"></script>
 <script src="js/app.js"></script>