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/devices/api.bru

@@ -1,5 +1,5 @@
 meta {
-  name: "Bookmann Device Management API"
+  name: "Bookhoard Device Management API"
   type: "collection"
   environment: {
     development: {