feat: agregar clase PasswordHasher para el hash de contraseñas

.vscode/settings.json

@@ -8,5 +8,6 @@
     ],
     "yaml.schemas": {
         "https://raw.githubusercontent.com/doanthuanthanh88/testapi6/main/schema.json": "*.yaml"
-    }
+    },
+    "cmake.sourceDirectory": "C:/Users/Mendez/Documents/Practicas de programacion/Proyecto-Hackathon (ITC)/hackathon-sfc-a9a4cee23109413188ee35ceac01dc07/windows"
 }

lib/core/security/password_hasher.dart

@@ -0,0 +1,13 @@
+import 'dart:convert';
+
+import 'package:crypto/crypto.dart';
+
+class PasswordHasher {
+  static const String _salt = 'waste-notify-local-salt-v1';
+
+  static String hash(String password) {
+    final normalized = password.trim();
+    final bytes = utf8.encode('$_salt:$normalized');
+    return sha256.convert(bytes).toString();
+  }
+}