Adds opt-in extension package internal/automc/ that:
- Subscribes to Postgres notifications on a 'servers' table and pushes
route changes into server.Routes (no file I/O, no fsnotify).
- Provides a WakerFunc that POSTs to a configurable HTTP control plane
(server-manager) and polls until state=running.
When AUTOMC_DSN is unset, Wire() is a no-op and the binary behaves
exactly like upstream itzg/mc-router. Single patch site in main.go
(import + 4-line call) keeps upstream rebases trivial.
See docs/AUTOMC.md for env vars and the expected DB schema/trigger.