#4635 Docs: hot-reload manual page lists which serve settings reload, including grant settings and admin removal

swamp-club#4588, #4602 and #4604 made most of serve.yaml apply on swamp serve reload. The manual page content/manual/reference/swamp-serve/hot-reload.md describes reloading extensions and grants but does not list which settings a reload applies and which need a restart.

Suggested content:

• A table of serve.yaml settings: applied on reload, needs a restart (listener, TLS, auth mode, OAuth client, datastore, heartbeat-interval, stale-ttl, remote-only, adding an admin), startup-only.
• Grant settings (#4604): grant-reload, grants-file, grants-dir and the three explicit-grant rules apply on reload; a grant source startup would refuse refuses the whole reload.
• Admins: removing an admin applies on reload (on the node leading grant writes in team mode; a follower applies it when it takes the lead); adding one needs a restart.
• How to read the reload report: applied, needs restart (with reason), overridden by a flag or environment variable.