test: add comprehensive authentication state tests

Add unit tests for all authentication flows in the Core:
- Login: loading state, success/failure handling, error clearing
- Logout: session cleanup, error handling
- Set password: initial password setup flow
- Update password: password change with validation
- Check requires password: state management

Tests are colocated with the auth handler code following Rust conventions.

Signed-off-by: Jan Zachmann <50990105+JanZachmann@users.noreply.github.com>

Author: JanZachmann

src/app/src/lib.rs

@@ -9,9 +9,6 @@ pub mod update;
 #[cfg(target_arch = "wasm32")]
 pub mod wasm;
 
-#[cfg(test)]
-mod tests;
-
 use crux_core::Command;
 
 // Using deprecated Capabilities API for Http (kept for Effect enum generation)