Updated Authentication Navigation

Authentication screens are now organized in a dedicated navigation stack with improved email handling and updated statistics labels.

Improvements

• Authentication flow screens (Login, Register, Reset Password) have been grouped into a dedicated navigation stack for clearer navigation.

• Login screen now accepts an email parameter for navigation instead of username, aligning data handling with user input.

• Settings screen displays user email instead of username for clearer user identification.

• Statistics screen updated the label from 'Representação Pessoal' to 'Concordância de Propostas' to better reflect the displayed data.