feat: support rich Menu action content

[artiphishle]

Summary

• replace the unused minimal Menu item shape with structured actions
• add MenuAction with title, description, leading, trailing, selected, disabled, intent, and activate
• render menu rows with layout primitives instead of nesting arbitrary content inside Text
• keep Surface-owned menu mechanics: trigger measurement, portal rendering, focus scope, keyboard navigation, escape handling, outside dismiss, and close-on-select behavior
• export MenuAction and MenuActionIntent from the component and root barrels
• add a patch changeset

Closes #56.

Notes

This intentionally does not preserve the previous items / label API because Surface Menu has not been consumed yet. This PR uses the opportunity to make the first real public API cleaner:

• actions instead of items
• title instead of label
• activate instead of onPress
• dismiss instead of onDismiss
• intent: 'default' | 'danger' instead of a broad color API

The existing MenuItem export remains as an alias of MenuAction for compatibility with the current barrel naming, but MenuAction is the preferred type name.

Verification

Not run locally in this environment because the connected GitHub API path cannot execute repo commands. Please run before merge:

bun run build
bun run lint:fix
bun run test