refactor: avoid synchronous state updates in useEffect (#1408)

Fixes a cascading render warning caused by calling `handleLogin`
synchronously inside a mounting effect.

Changes:
- Decoupled the API login logic from the manual UI loading trigger.
- Initialized `isLoggingIn` state based on URL parameters to prevent
  an immediate rerender on mount.
- Extracted `performLogin` to handle the side effect without
  triggering synchronous state updates.

Signed-off-by: Jasmina <jasmina.piric@secomind.com>
Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: JasminaPiric