Restructure solution layout by module

src/Zastava/StellaOps.Zastava.Webhook/Certificates/CsrCertificateSource.cs

@@ -0,0 +1,25 @@
+using System.Security.Cryptography.X509Certificates;
+using StellaOps.Zastava.Webhook.Configuration;
+
+namespace StellaOps.Zastava.Webhook.Certificates;
+
+/// <summary>
+/// Placeholder implementation for CSR-based certificate provisioning.
+/// </summary>
+public sealed class CsrCertificateSource : IWebhookCertificateSource
+{
+    private readonly ILogger<CsrCertificateSource> _logger;
+
+    public CsrCertificateSource(ILogger<CsrCertificateSource> logger)
+    {
+        _logger = logger;
+    }
+
+    public bool CanHandle(ZastavaWebhookTlsMode mode) => mode == ZastavaWebhookTlsMode.CertificateSigningRequest;
+
+    public X509Certificate2 LoadCertificate(ZastavaWebhookTlsOptions options)
+    {
+        _logger.LogError("CSR certificate mode is not implemented yet. Configuration requested CSR mode.");
+        throw new NotSupportedException("CSR certificate provisioning is not implemented (tracked by ZASTAVA-WEBHOOK-12-101).");
+    }
+}