Autofocus environment name in creation modal

[abhishekp106]

Summary

• Delegate focus from the handoff environment creation modal wrapper into the embedded environment form
• Add a regression test that confirms focusing the popup modal lands on the environment name editor

Test

• cargo test -p warp settings_view::handoff_environment_creation_modal::tests::test_modal_focuses_environment_name_editor_when_focused

This PR was created by Oz (running Codex).