Don't mock server-only properties on client-side

Editor assessment

The subject states the boundary precisely — server-only properties are not mocked on the client — so the header communicates the fix and the cross-environment leak it closes without the diff, and fix(nuxt3) classifies and locates it correctly. Hygiene is clean: imperative mood, no trailing period, sensible length, no ticket junk. No body is needed for a contained environment fix, and no footer is required. A line on the failures the improper mocking caused, such as runtime crashes in the browser, would add depth; the message is already clear and publishable.