Add itsdangerous dependency to requirements.txt

- Included `itsdangerous>=2.1.2` in `requirements.txt` to support secure cookie handling and data serialization in the application.

Author: TMHSDigital

requirements.txt

@@ -1,4 +1,5 @@
 httpx>=0.27.0
+itsdangerous>=2.1.2
 python-dotenv>=1.0.1
 pytest>=8.0.0
 pytest-cov>=5.0.0