Fix Chrome Custom Tab auto-dismissal after verification on Android

[seftena]

What

After verification completes, the Chrome Custom Tab was not dismissing automatically —
the user had to manually tap Done/Dismiss. iOS handles this natively via
ASWebAuthenticationSession. Android requires the SDK to manage it explicitly.

Root Cause

IDmeRedirectActivity was calling finish() after receiving the redirect, which popped
it off the stack but revealed the Custom Tab sitting behind it. Nothing was bringing
the calling app back to the foreground.

Fix

• Store a WeakReference to the calling Activity in IDmeAuthManager when the auth
  flow starts, cleared on completion
• In IDmeRedirectActivity, after the redirect is received, fire an explicit intent
  back to the calling Activity with FLAG_ACTIVITY_CLEAR_TOP before calling finish(),
  which removes the Custom Tab from the back stack and returns the user to the app

Files changed

• IDmeAuthManager.kt — added WeakReference to calling Activity
• IDmeRedirectActivity.kt — added foreground restore on redirect