Ongoing REST API documentation improvements

**Describe the solution you'd like **
Ongoing OWASP Nest REST API documentation improvements (docs-only). Include details like pagination, auth notes, request/response examples, common errors, consistent formatting, etc.

**Are you going to work on implementing this?**

- [x] Yes
- [ ] No

**Additional context**
Each docs PR will link back to the tracking issue using `Refs #` (not `Fixes #`) so it doesn’t auto-close on merge.