Refactor: Server-Settings von appsettings.json in DB-Tabelle (server_settings)

- Neuer ServerSettingsService: zentrale Settings in SQLite mit In-Memory-Cache
- Auto-Migration: bestehende appsettings.Production.json wird einmalig in DB übernommen
- Alle Services umgestellt: IConfiguration → ServerSettingsService (dynamisch, kein Neustart)
- Port bleibt als einziges Setting in appsettings.Production.json (erfordert Neustart)
- ServerSettingsEndpoint: liest/schreibt DB statt JSON-Datei, Port als Sonder-Setting
- IConfiguration komplett entfernt aus allen Services (ChatService, ToolService, AnthropicService,
  OpenAiService, KreaService, TelegramService, KeyScannerService, GitHubEventScannerService)
- AuthMiddleware: KreaApiKey dynamisch aus DB
- appsettings.json bereinigt: nur noch Port und Logging
- Dokumentation aktualisiert (ARCHITECTURE.md, ARCHITECTURE_QUICK.md, README.md)

Services/KreaService.cs

@@ -14,9 +14,11 @@ namespace Gott.Services
     public class KreaService
     {
         private readonly IHttpClientFactory _httpFactory;
-        private readonly string _token;
+        private readonly ServerSettingsService _settings;
         private readonly string _imagesDir;
 
+        private string _token => _settings.Get("KreaToken");
+
         private const string BASE_URL = "https://api.krea.ai";
 
         public static readonly Dictionary<string, string> IMAGE_MODELS = new Dictionary<string, string>
@@ -47,10 +49,10 @@ namespace Gott.Services
 
         public bool IsConfigured => !string.IsNullOrWhiteSpace(_token);
 
-        public KreaService(IHttpClientFactory httpFactory, string token, string dataDir)
+        public KreaService(IHttpClientFactory httpFactory, ServerSettingsService settings, string dataDir)
         {
             _httpFactory = httpFactory;
-            _token = token;
+            _settings = settings;
             _imagesDir = Path.Combine(dataDir, "images");
             Directory.CreateDirectory(_imagesDir);
         }