[wiperpaul]

Summary

• Add a read-only preview for the currently selected schema.
• Show the schema name, label count, resolved colors, and number-key mappings in a responsive modal.
• Allow the preview to be closed without affecting the current annotation session.
• Add end-to-end coverage and document the new feature.

This gives users a quick way to understand a loaded schema without inspecting its YAML file or leaving the annotation workspace.

Testing

• uv run pre-commit run --all-files
• Chromium end-to-end test covering opening, displaying, and closing the schema preview
• git diff --check

Screenshots