fix(super-editor): restore toolbar dropdown keyboard focus

[sergiogomes]

Summary

• Opens toolbar dropdowns with Enter and Space.
• Restores focus to the dropdown trigger when Escape closes the menu.
• Adds unit coverage for dropdown keyboard activation and Escape focus restoration.

Test plan

• Targeted toolbar tests:

pnpm exec vitest run packages/super-editor/src/editors/v1/components/toolbar/ButtonGroup.test.js packages/super-editor/src/editors/v1/components/toolbar/ToolbarDropdown.test.js

• pnpm run format:check
• pnpm run lint
• Manual: open font dropdown, navigate with arrow keys, press Escape, confirm focus returns to the trigger.

Note: local commands printed existing warnings outside the toolbar files touched in this PR.

[sergiogomes]

Rebased onto the latest main and resolved the ButtonGroup.test.js conflict by keeping both the upstream argument-forwarding tests and this PR’s dropdown keyboard activation coverage.