feat: API-Payload-Logging in data/logs/ für Debugging

- LogPayload() schreibt den kompletten Claude-API-Request als indented JSON
- Dateiname: <unixtime>-<sessionId>-<chainId>-iter<N>-payload.json
- Beide Pfade abgedeckt: StreamChat (Web) + ChatNonStreaming (Telegram/Cronjobs)
- try/catch: Logging-Fehler crashen nie die App

Services/AnthropicService.cs

@@ -94,7 +94,8 @@ public class AnthropicService
                 }
 
                 var client = CreateClient();
-                var json = JsonSerializer.Serialize(payload);
+                var json = JsonSerializer.Serialize(payload, new JsonSerializerOptions { WriteIndented = true });
+                LogPayload(json, sessionId, chainId, iterations);
                 var httpContent = new StringContent(json, Encoding.UTF8, "application/json");
 
                 var httpResp = await client.SendAsync(
@@ -292,7 +293,8 @@ public class AnthropicService
                 }
 
                 var client = CreateClient();
-                var json = JsonSerializer.Serialize(payload);
+                var json = JsonSerializer.Serialize(payload, new JsonSerializerOptions { WriteIndented = true });
+                LogPayload(json, ctx.SessionId, ctx.ChainId, iterations);
                 var httpContent = new StringContent(json, Encoding.UTF8, "application/json");
 
                 var httpResp = await client.SendAsync(
@@ -414,6 +416,19 @@ public class AnthropicService
         return finalText.Length > 0 ? finalText.ToString() : "(Keine Textantwort)";
     }
 
+    private static void LogPayload(string json, string sessionId, string chainId, int iteration)
+    {
+        try
+        {
+            var logsDir = Path.Combine(AppContext.BaseDirectory, "data", "logs");
+            Directory.CreateDirectory(logsDir);
+            var timestamp = DateTimeOffset.UtcNow.ToUnixTimeSeconds();
+            var fileName = $"{timestamp}-{sessionId}-{chainId}-iter{iteration}-payload.json";
+            File.WriteAllText(Path.Combine(logsDir, fileName), json);
+        }
+        catch { /* Logging darf nie die App crashen */ }
+    }
+
     private async Task FinalizeChain(ChainRecord chain, TokenUsage usage, int iterations, string stopReason, System.Diagnostics.Stopwatch sw, string streamErrorInfo = null)
     {
         chain.InputTokens = usage.InputTokens;