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)

Endpoints/ChatEndpoint.cs

@@ -10,7 +10,6 @@ using Gott.Services;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Routing;
-using Microsoft.Extensions.Configuration;
 
 namespace Gott.Endpoints;
 
@@ -22,7 +21,7 @@ public static class ChatEndpoint
         app.MapPost("/api/chat/stop", HandleStop);
     }
 
-    private static async Task HandleChat(HttpRequest req, HttpResponse res, IConfiguration config, ChatService chatService, DatabaseService db, StreamingTracker streamingTracker, AnthropicService anthropic, OpenAiService openAi, RemoteConnectionManager remoteMgr, EmbeddingBackgroundService embeddingBg, CancellationToken cancellationToken)
+    private static async Task HandleChat(HttpRequest req, HttpResponse res, ServerSettingsService settings, ChatService chatService, DatabaseService db, StreamingTracker streamingTracker, AnthropicService anthropic, OpenAiService openAi, RemoteConnectionManager remoteMgr, EmbeddingBackgroundService embeddingBg, CancellationToken cancellationToken)
     {
         var body = await JsonSerializer.DeserializeAsync<ChatRequest>(req.Body);
         if (body == null)
@@ -61,7 +60,7 @@ public static class ChatEndpoint
             return;
         }
 
-        var maxIterations = config.GetValue<int>("MaxIterations", 100);
+        var maxIterations = settings.GetInt("MaxIterations", 100);
 
         var hasRemote = remoteMgr.GetBySessionId(sessionId) != null;
         var ctx = await chatService.PrepareContext(sessionId, userId, maxIterations, planMode: body.PlanMode, hasRemoteConnection: hasRemote);