Unify SHA256 hash and hex usages (#687)

bitchat/Utils/Data+SHA256.swift

@@ -0,0 +1,22 @@
+//
+//  Data+SHA256.swift
+//  bitchat
+//
+//  Created by Islam on 26/09/2025.
+//
+
+import struct Foundation.Data
+import struct CryptoKit.SHA256
+
+extension Data {
+    /// Returns the hex representation of SHA256 hash
+    func sha256Fingerprint() -> String {
+        // Implementation matches existing fingerprint generation in NoiseEncryptionService
+        sha256Hash().hexEncodedString()
+    }
+    
+    /// Returns the SHA256 hash wrapped in Data
+    func sha256Hash() -> Data {
+        Data(SHA256.hash(data: self))
+    }
+}