VSN-2844/ feat: initial project setup with auth flow and navigation skeleton
This mr includes initial setup of the vsn-staff-mobile app :
- Expo SDK 54 project
- Full auth flow: login, JWT decode, session persistence (AsyncStorage + rememberMe)
- AuthGuard protecting private routes with redirect to /auth/login
- Navigation skeleton: 5-tab bar (Demandes, Documents, Home, Tickets, Profile)
- ThemeContext (dark/light), Axios instance configured, base UI components (Input, Button, Checkbox, ErrorMessage)
- GitLab CI pipeline added