Rename the injected context-menu action from 'Create guest link' to
'ShareLink' and swap its cloned copy icon (content_copy) for the share
icon, matching the other menu items' style.
Replace the placeholder scaffold README with a user-facing one describing
what the plugin does, the server-side guest confinement, configuration,
and the known Jellyfin cast/crew tag bug (jellyfin/jellyfin#14926).
Includes fix for redemption failing with DbUpdateConcurrencyException:
change the guest password before applying the user policy, since
UpdatePolicyAsync bumps the user's EF concurrency token and a stale
instance then breaks ChangePassword.
Franciskid