feat: add EPBundleSelectionIndicator for bundle option styling

[field123]

Summary

• Adds EPBundleSelectionIndicator code component that bridges BundleOptionContext.isSelected to a data-selected HTML attribute
• Allows Plasmic designers to style radio/checkbox indicators inside EPBundleOptionTrigger using CSS selectors on data-selected
• Supports previewState prop for design-time preview of selected/unselected states, with mock data fallback in the editor

Test plan

• 9 unit tests added covering rendering, data-selected toggle, aria-hidden, className, previewState overrides, mock fallback, and no-context behavior
• All 847 tests pass
• TypeScript build succeeds
• Insert component inside an EPBundleOptionTrigger in Plasmic studio, style as radio circle, verify data-selected toggles on click