Restructure solution layout by module

src/__Libraries/StellaOps.Cryptography/PasswordHashAlgorithms.cs

@@ -0,0 +1,23 @@
+using System;
+
+namespace StellaOps.Cryptography;
+
+/// <summary>
+/// Well-known identifiers for password hashing algorithms supported by StellaOps.
+/// </summary>
+public static class PasswordHashAlgorithms
+{
+    public const string Argon2id = "argon2id";
+    public const string Pbkdf2Sha256 = "pbkdf2-sha256";
+
+    /// <summary>
+    /// Converts the enum value into the canonical algorithm identifier string.
+    /// </summary>
+    public static string ToAlgorithmId(this PasswordHashAlgorithm algorithm) =>
+        algorithm switch
+        {
+            PasswordHashAlgorithm.Argon2id => Argon2id,
+            PasswordHashAlgorithm.Pbkdf2 => Pbkdf2Sha256,
+            _ => throw new ArgumentOutOfRangeException(nameof(algorithm), algorithm, "Unsupported password hash algorithm.")
+        };
+}