[Bug] Inline styles cannot exit to normal text at paragraph end

[peiyucn]

Description

When the cursor is inside an inline style (bold, italic, strikethrough, inline code, etc.) at the end of a paragraph with nothing following, pressing right arrow or typing does not exit the mark. The cursor remains stuck inside the formatting.

This affects all inline marks, not just inline code. The root cause is that the mark boundary is inclusive (marks are sticky at the right edge), and there is no mechanism to break out when at a paragraph end.

Steps to Reproduce

1. Open the Crepe playground
2. Apply any inline style (bold with Mod-b, code with Mod-e, etc.) at the end of a paragraph
3. Try to type normal text after the styled text
4. Observe: text continues in the applied style

Expected

A way to exit inline mark mode at paragraph end (e.g., pressing right arrow or typing should break out of the mark).