SkeetView: Refactor layout for better thread line continuity
Separate the layout logic for nested and top-level posts to ensure the thread line spans the full height of the post.
- Use a simple `Column` layout for nested (embedded) posts.
- Use a two-column `Row` layout for top-level posts, allowing the avatar and thread line to span the full vertical height of the content.
- Move `SkeetReason` inside the right-hand content column for top-level posts.
- Adjust padding and vertical divider constraints to improve the visual connection between posts in a thread.