feat: Serper Web Search als Agent-Tool

- ToolService: serper_web_search Tool-Definition + ExecuteSerperWebSearch()
  Google-Suche via Serper.dev API mit Titel, Link, Snippet
  Knowledge Graph + Answer Box + organische Ergebnisse
- AgentRecord: UseSerperSearch Property (Default: false)
- DB-Migration: use_serper_search Spalte
- AnthropicService + ChatService: useSerperSearch Parameter durchreichen
- ChatEndpoint + AgentEndpoint: useSerperSearch in API
- Frontend: Checkbox, Badge (Serper Search), laden/speichern
- Aktivierung: Agent-Checkbox + SerperApiKey in Server-Einstellungen

wwwroot/js/cards.js

@@ -109,6 +109,7 @@ function buildAgentCard(agent, skills) {
   if (agent.useMemory) badges.push('<span class="badge badge-feature" title="Zugriff auf Erinnerungen (Memory-Tools)"><i class="fa fa-database"></i> Erinnerungen</span>');
   if (agent.useAutoContext) badges.push('<span class="badge badge-feature" title="Relevante Erinnerungen werden automatisch abgerufen"><i class="fa fa-magic"></i> Auto-Kontext</span>');
   if (agent.useGitHubSearch) badges.push('<span class="badge badge-feature" title="Öffentlichen Code auf GitHub durchsuchen"><i class="fa fa-github"></i> GitHub Search</span>');
+  if (agent.useSerperSearch) badges.push('<span class="badge badge-feature" title="Google-Suche via Serper.dev API"><i class="fa fa-google"></i> Serper Search</span>');
   if (agent.webSearchVersion) {
     const wsYear = agent.webSearchVersion.includes('2025') ? 'Version 2025' : 'v2026';
     badges.push(`<span class="badge badge-feature" title="Web-Suche - ${wsYear}"><i class="fa fa-search"></i> Web-Suche</span>`);