OPC # 0001: Extract Clarity into standalone repo

Clarity.Server/Data/BlindIndexHelper.cs

@@ -0,0 +1,37 @@
+using System.Security.Cryptography;
+using System.Text;
+
+namespace Clarity.Server.Data;
+
+public static class BlindIndexHelper
+{
+    // In a real environment, this "Pepper" comes from your TenantKeyProvider or Vault!
+    // It must NEVER change once records are written, or searches will break.
+    public static string Compute(string? input, byte[] staticPepper)
+    {
+        if (string.IsNullOrWhiteSpace(input)) return string.Empty;
+
+        // 1. Normalize (Remove dashes, spaces, make uppercase)
+        var normalized = input.Replace("-", "").Replace(" ", "").ToUpperInvariant();
+
+        // 2. Hash using HMAC-SHA256 and the static Pepper
+        using var hmac = new HMACSHA256(staticPepper);
+        var hashBytes = hmac.ComputeHash(Encoding.UTF8.GetBytes(normalized));
+
+        // 3. Return Base64 for database storage
+        return Convert.ToBase64String(hashBytes);
+    }
+}
+
+[AttributeUsage(AttributeTargets.Property)]
+public class BlindIndexedAttribute : Attribute
+{
+    public string TargetPropertyName { get; }
+
+    public BlindIndexedAttribute(string targetPropertyName)
+    {
+        TargetPropertyName = targetPropertyName;
+    }
+}
+
+