feat(theme): add top placement for sections

- Add `placement: top|bottom` to the section frontmatter
- Override `DocContent` to render hoisted bands under the page title
- Derive the zebra stripe from list position so split bands stay continuous
- Opt marketing bands out of doc typography with `rp-not-doc`
- Point the legal and privacy contact address at legal@onixbyte.com
- Condense the products pages' body copy into their section frontmatter

docs/zh-hans/legal/terms.md

@@ -57,7 +57,7 @@ OnixByte 名称、标识及本网站的设计归我们所有。我们发布的
 
 ## 联系方式
 
-**business@onixbyte.com**
+**legal@onixbyte.com**
 
 长沙曜珀科技有限公司
 中国湖南省