fix: refresh bench REST routes after activation

[chubes4]

Summary

• Refresh the REST server after wordpress.bench activates mounted plugins late in a runtime.
• Covers plugins that register routes on rest_api_init, matching normal WordPress activation/load behavior more closely.
• Extends the bench fixture smoke to assert a plugin REST route is visible to bench workloads.

Testing

• npm run build
• npm run recipe-bench-smoke

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Diagnosed the late plugin activation REST route gap, drafted the route refresh fix, and added smoke coverage. Chris remains responsible for review and merge.