Move relationship types + dashboard recent off the machines blueprint

- Add /api/assets/relationshiptypes (GET/POST) serving RelationshipType; point
  relationshipTypesApi at it instead of the legacy /api/machines blueprint.
- Dashboard recent-devices widget reads assetsApi.list (asset shape) instead
  of machinesApi.

No frontend code references machinesApi anymore.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/api/index.js

@@ -176,10 +176,10 @@ export const computersApi = {
 // Relationship Types API
 export const relationshipTypesApi = {
   list() {
-    return api.get('/machines/relationshiptypes')
+    return api.get('/assets/relationshiptypes')
   },
   create(data) {
-    return api.post('/machines/relationshiptypes', data)
+    return api.post('/assets/relationshiptypes', data)
   }
 }