Fix Markdown typography spacing.
- Adds an independent line-height control.
- Applies block spacing to paragraphs, lists, list items, headings, quotes, code blocks, and separators.
- Preserves settings written by earlier versions with an automatic line-height default.
- Updates bilingual documentation and visual examples.
修复行间距和段落间距：新增独立行间距设置，并让块间距覆盖 Markdown 段落、列表、标题、引用和代码块。