Rename API test collection references: Bookmann → Bookhoard

Bruno API test updates:
- Update test assertions: X-Bookmann-* → X-Bookhoard-*
- Update variable names and references in test scripts
- Update documentation and comments in API tests

This is part 4 of the project rename to Bookhoard.

bruno/kobo/initialization.bru

@@ -17,5 +17,5 @@ assert {
   response.status == 200
   response.body.ContentId exists()
   response.body.Categories exists()
-  response.body.BookmannUUID exists()
+  response.body.BookhoardUUID exists()
 }