refactor(oidc): move OIDC module to versioned API path

- Move OIDC endpoints from gatehouse_app/api/oidc.py to gatehouse_app/api/v1/oidc.py
- Register OIDC discovery endpoint directly on app instead of separate blueprint
- Update service name from authy2-backend to secuird-backend in health check

gatehouse_app/api/__init__.py

@@ -10,7 +10,7 @@ api_bp = Blueprint("api", __name__)
 def health_check():
     """Health check endpoint."""
     return api_response(
-        data={"status": "healthy", "service": "authy2-backend"},
+        data={"status": "healthy", "service": "secuird-backend"},
         message="Service is running",
     )