refactor: Backend-Deduplizierung – Parameter-Objekte, Shared Helpers, KeyCheckDispatcher

- ToolDefinitionOptions + ToolExecutionContext ersetzen lange Parameterlisten in ToolService
- AppendToLastMessage-Helper in ChatService eliminiert 5x duplizierte Logik
- OpenAiService: ResolveProviderConfig + BuildApiMessages + ConvertToOpenAiTools statt doppeltem Code
- Tool-Definitionen aus einer Quelle (Anthropic→OpenAI Konvertierung statt hardcodierter Liste)
- KeyCheckDispatcher zentralisiert Key-Check-Dispatch (ApiKeysEndpoint, KeyScanner, GitHubEventScanner)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Services/KeyCheckDispatcher.cs

@@ -0,0 +1,96 @@
+using System.Net.Http;
+using System.Threading.Tasks;
+
+namespace Gott.Services;
+
+/// <summary>
+/// Normalisiertes Key-Check-Ergebnis für alle Provider.
+/// Provider-spezifische Details über ProviderResult (cast zum konkreten Typ).
+/// </summary>
+public class UnifiedKeyCheckResult
+{
+    /// <summary>Normalisierter DB-Status: "valid", "invalid", "rate_limited", "quota_exceeded", "error"</summary>
+    public string DbStatus { get; set; }
+    public string Message { get; set; }
+    public string Plan { get; set; }
+    public double? Usage7d { get; set; }
+    public double? Usage5h { get; set; }
+
+    /// <summary>Original-Result des Providers (KeyCheckResult, OpenAiCheckResult, etc.)</summary>
+    public object ProviderResult { get; set; }
+}
+
+/// <summary>
+/// Zentraler Dispatcher für Key-Checks aller Provider.
+/// Normalisiert den Status und gibt ein einheitliches Ergebnis zurück.
+/// Eliminiert die wiederholten switch/if-Ketten in ApiKeysEndpoint, KeyScannerService, GitHubEventScannerService.
+/// </summary>
+public static class KeyCheckDispatcher
+{
+    /// <summary>
+    /// Prüft einen API-Key anhand des Providers.
+    /// Provider: "anthropic", "openai", "google", "stripe".
+    /// Gibt null zurück bei unbekanntem Provider.
+    /// </summary>
+    public static async Task<UnifiedKeyCheckResult> CheckByProvider(IHttpClientFactory httpFactory, string provider, string apiKey)
+    {
+        switch (provider)
+        {
+            case "anthropic":
+            {
+                var r = await AnthropicKeyChecker.CheckKeyAsync(httpFactory, apiKey);
+                return new UnifiedKeyCheckResult
+                {
+                    DbStatus = (r.Status == "ok" || r.Status == "usage_limited") ? "valid" : r.Status,
+                    Message = r.Message, Plan = r.Plan,
+                    Usage7d = r.Usage7d, Usage5h = r.Usage5h,
+                    ProviderResult = r
+                };
+            }
+            case "openai":
+            {
+                var r = await OpenAiKeyChecker.CheckKeyAsync(httpFactory, apiKey);
+                return new UnifiedKeyCheckResult
+                {
+                    DbStatus = r.Status == "ok" ? "valid" : r.Status,
+                    Message = r.Message, Plan = r.Message,
+                    ProviderResult = r
+                };
+            }
+            case "google":
+            {
+                var r = await GoogleKeyChecker.CheckKeyAsync(httpFactory, apiKey);
+                return new UnifiedKeyCheckResult
+                {
+                    DbStatus = r.Status == "ok" ? "valid" : r.Status,
+                    Message = r.Message, Plan = r.Message,
+                    ProviderResult = r
+                };
+            }
+            case "stripe":
+            {
+                var r = await StripeKeyChecker.CheckKeyAsync(httpFactory, apiKey);
+                return new UnifiedKeyCheckResult
+                {
+                    DbStatus = r.Status == "ok" ? "valid" : r.Status,
+                    Message = r.Message, Plan = r.IsLiveKey ? "Live" : "Test",
+                    ProviderResult = r
+                };
+            }
+            default:
+                return null;
+        }
+    }
+
+    /// <summary>
+    /// Prüft einen API-Key anhand des Key-Typs (z.B. "openai_project", "anthropic_oauth").
+    /// Nutzt KeyPatterns.GetCheckerProvider() für die Zuordnung.
+    /// Gibt null zurück wenn kein Checker für den Typ existiert.
+    /// </summary>
+    public static Task<UnifiedKeyCheckResult> CheckByKeyType(IHttpClientFactory httpFactory, string keyType, string apiKey)
+    {
+        var provider = KeyPatterns.GetCheckerProvider(keyType);
+        if (provider == null) return Task.FromResult<UnifiedKeyCheckResult>(null);
+        return CheckByProvider(httpFactory, provider, apiKey);
+    }
+}