feat: Episode Breakout View in Card View with Scene Drill-Down

[stultus]

As a writer planning a multi-episode project,
the writer wants a Card View that displays episodes as individual cards with the ability to drill down into scene cards within each episode,
so that episodes can be outlined first and scenes can be explored hierarchically without switching views.

Context

The current Card View supports a Scene Breakout only. Writers who plan top-down need an Episode-level entry point. A hierarchical drill-down (Episode → Scenes) provides a more natural information architecture than a flat toggle, preserves context as the writer navigates, and aligns with how episodic content is structured.

Acceptance Criteria

1. Card View opens at the Episode level by default for projects structured into episodes.
2. Each episode card displays episode-level metadata (title, number, synopsis, status, scene count).
3. Writers can create, edit, reorder, and delete episode cards from this view.
4. Selecting an episode card drills down into a Scene Card view scoped to that episode.
5. A clear back action or breadcrumb allows the writer to return from the Scene view to the Episode view.
6. Scene cards within a drilled-down episode retain all existing Scene Breakout functionality (create, edit, reorder, delete).
7. Navigation state (current level and selected episode) persists across sessions per project.