feat: GitHub Code Search als Agent-Tool + Dashboard-Badges

- UseGitHubSearch Property im AgentRecord (Default: false)
- DB-Migration: use_github_search Spalte in agents
- Checkbox im Agent-Formular (Standard: unchecked)
- Tool nur aktiv wenn Agent-Checkbox UND GitHubToken konfiguriert
- includeGitHubSearch Parameter durch StreamChat/AddToolsToPayload
- Dashboard-Badges: 🔮 Auto-Kontext + 🐙 GitHub Search

Endpoints/AgentEndpoint.cs

@@ -65,6 +65,7 @@ public static class AgentEndpoint
                 a.UseUserInfo,
                 a.UseMemory,
                 a.UseAutoContext,
+                a.UseGitHubSearch,
                 a.UseWebSearch,
                 a.WebSearchVersion,
                 a.AllowUserChoice,
@@ -121,6 +122,7 @@ public static class AgentEndpoint
             UseUserInfo = !body.TryGetProperty("useUserInfo", out var uu) || uu.GetBoolean(),
             UseMemory = !body.TryGetProperty("useMemory", out var um) || um.GetBoolean(),
             UseAutoContext = !body.TryGetProperty("useAutoContext", out var uac) || uac.GetBoolean(),
+            UseGitHubSearch = body.TryGetProperty("useGitHubSearch", out var ughs) && ughs.GetBoolean(),
             UseWebSearch = body.TryGetProperty("webSearchVersion", out var wsv) && !string.IsNullOrEmpty(wsv.GetString()),
             WebSearchVersion = body.TryGetProperty("webSearchVersion", out var wsv2) ? wsv2.GetString() ?? "" : "",
             AllowUserChoice = !body.TryGetProperty("allowUserChoice", out var auc) || auc.GetBoolean(),
@@ -163,6 +165,7 @@ public static class AgentEndpoint
         if (body.TryGetProperty("useUserInfo", out var uu)) agent.UseUserInfo = uu.GetBoolean();
         if (body.TryGetProperty("useMemory", out var um)) agent.UseMemory = um.GetBoolean();
         if (body.TryGetProperty("useAutoContext", out var uac)) agent.UseAutoContext = uac.GetBoolean();
+        if (body.TryGetProperty("useGitHubSearch", out var ughs)) agent.UseGitHubSearch = ughs.GetBoolean();
         if (body.TryGetProperty("webSearchVersion", out var wsv))
         {
             agent.WebSearchVersion = wsv.GetString() ?? "";