feat(infrastructure): register RsaKeyService in DI

NEW/src/JdeScoping.Core/Options/RsaKeyOptions.cs

@@ -0,0 +1,15 @@
+namespace JdeScoping.Core.Options;
+
+/// <summary>
+/// Configuration options for RSA key service.
+/// </summary>
+public class RsaKeyOptions
+{
+    public const string SectionName = "RsaKey";
+
+    /// <summary>
+    /// Path to store the RSA private key file.
+    /// Defaults to "data/rsa-key.bin" relative to app directory.
+    /// </summary>
+    public string KeyFilePath { get; set; } = "data/rsa-key.bin";
+}