Background services no longer run their work on the mesh router

The mesh router's only job is to route messages — but several background services (the plugin default-install seed, log-incident filing, GitHub sync writes, and one-shot node reads) were issuing their work directly on it. Every such operation competed with routing itself and produced a steady stream of router-traffic error logs (hundreds per day on a busy portal).

All of these now issue their work on the dedicated off-router work hub, so routing stays responsive under load and the error stream disappears. The router-traffic detector also no longer flags the router's own undeliverable-message notices, so the remaining reports point at genuine problems only.