feat: GitHub Event Scanner - Echtzeit-Monitoring öffentlicher Pushes

- Neuer GitHubEventScannerService (BackgroundService)
  - Pollt /events API alle 30s, filtert PushEvents
  - Lädt Head-Commit-Diffs, scannt nach Key-Patterns
  - Ringbuffer (10k IDs) für Event-Deduplication
  - Gefundene Keys werden sofort geprüft (AnthropicKeyChecker)
  - Rate-Limit-Handling (403/429 → Pause bis Reset)
- Feature-Toggle in Server-Einstellungen (GitHubEventScanner)
- Status-Endpoint + Log-Endpoint (/api/admin/api-keys/event-scanner/*)
- Live-Status in API-Keys-Seite mit klappbarem Log
- Auto-Refresh alle 30s
- Plans/ in .gitignore

Endpoints/ServerSettingsEndpoint.cs

@@ -35,6 +35,7 @@ public static class ServerSettingsEndpoint
         new SettingDefinition("SerperApiKey", "string", "", "Serper.dev API-Key für Google-Suche (Key-Scanner)", "password"),
         new SettingDefinition("ProxyUrl", "string", "", "HTTP/SOCKS Proxy für alle Requests (z.B. socks5://127.0.0.1:1080)", "text"),
         new SettingDefinition("ScanIntervalHours", "int", 0, "Key-Scanner Intervall in Stunden (0 = nur manuell)", "number"),
+        new SettingDefinition("GitHubEventScanner", "bool", false, "GitHub Event Scanner (Echtzeit-Monitoring öffentlicher Pushes)", "toggle"),
     };
 
     public static void MapServerSettingsEndpoints(this WebApplication app)