hscontrol: use EmbedObject for node logging

Replace manual Uint64("node.id")/Str("node.name") field patterns with
EmbedObject(node) which automatically includes all standard node fields
(id, name, machine key, node key, online status, tags, user).

This reduces code repetition and ensures consistent logging across:
- state.go: Connect/Disconnect, persistNodeToDB, AutoApproveRoutes
- auth.go: handleLogout, handleRegisterWithAuthKey

hscontrol/db/ip.go

@@ -283,7 +283,7 @@ func (db *HSDatabase) BackfillNodeIPs(i *IPAllocator) ([]string, error) {
 		}
 
 		for _, node := range nodes {
-			log.Trace().Caller().Uint64("node.id", node.ID.Uint64()).Str("node.name", node.Hostname).Msg("IP backfill check started because node found in database")
+			log.Trace().Caller().EmbedObject(node).Msg("IP backfill check started because node found in database")
 
 			changed := false
 			// IPv4 prefix is set, but node ip is missing, alloc