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/en-gb/legal/privacy.md

@@ -75,7 +75,7 @@ those rights are not affected by anything in this policy.
 
 Questions about this policy, or about how we handle data:
 
-**business@onixbyte.com**
+**legal@onixbyte.com**
 
 Changsha Onix Byte Technology Co., Ltd
 Hunan Province, China

docs/en-gb/legal/terms.md

@@ -81,7 +81,7 @@ that means you accept the revised terms.
 
 ## Contact
 
-**business@onixbyte.com**
+**legal@onixbyte.com**
 
 Changsha Onix Byte Technology Co., Ltd
 Hunan Province, China