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/privacy.md

@@ -56,7 +56,7 @@ localStorage 键），但未经律师审阅。正式依赖前请交由法务检
 
 关于本政策，或关于我们如何处理数据：
 
-**business@onixbyte.com**
+**legal@onixbyte.com**
 
 长沙曜珀科技有限公司
 中国湖南省