feat: log failed webgui login attempts

Logs failed login attempts with the client IP address for security
monitoring purposes.

Cherry-picked from postalserver/postal PR postalserver#3221

Co-authored-by: olegbliaher <olegbliaher@users.noreply.github.com>
Co-authored-by: openhands <openhands@all-hands.dev>

Author: openhands-agent

app/controllers/sessions_controller.rb

@@ -12,6 +12,7 @@ def create
     flash[:remember_login] = true
     redirect_to_with_return_to root_path
   rescue Postal::Errors::AuthenticationError
+    Postal.logger.error "Invalid credentials for #{request.remote_ip}", component: "postal-web"
     flash.now[:alert] = "The credentials you've provided are incorrect. Please check and try again."
     render "new"
   end