feat(filmstrip): restore keyboard focus parity and add scrollNavigate event

[HeavyMedl]

This PR restores expected keyboard navigation behavior and introduces enhancements to the CdrFilmstrip.vue component for better tracking and developer ergonomics.

1. Restored feature parity with @rei/recommendations-slider

• When navigating via keyboard (arrow keys), the filmstrip now shifts focus to the next or previous frame, matching the behavior in the legacy @rei/recommendations-slider implementation.

2. New scrollNavigate event

• Introduces a new scrollNavigate event that emits when the user manually scrolls the filmstrip (e.g., via trackpad or scrollbar).
• The event is not emitted during programmatic scrolls triggered by:
  • Arrow button clicks
  • Keyboard focus navigation
• Payload includes:
  • event: original scroll event
  • index: the active frame index
  • model: the props of the frame at that index

3. Vue Styleguidist annotations

• Added missing annotations to the CdrFilmstripEngine.vue component for improved styleguide integration.