[management] Serve networks with peer-based routers from the SQLite network map (#7418)

The SQLite network-map query expanded a router's groups with from network_routers, json_each(peer_groups). That comma is an inner join, so a router row survives only when json_each returns at least one row. A router targeting an individual peer carries no groups — the write path stores NULL for a nil slice and '[]' for an empty one — and json_each yields nothing for either, so the join erased the router before it could be keyed by its peer. Postgres reads the same rows through a correlated subquery and was never affected.

The fix expands the groups with a left join, so the router survives with a NULL group_peers.peer_id and the existing scan loop keys it by router.Peer. Group routers still fan out one row per member.

management/internals/network_map_db/sqlite/network_router.go

@@ -11,9 +11,11 @@ import (
 )
 
 const (
+	// Outer join: a groupless router must survive.
 	GetNetworkRouterQuery = `
 	select public_id, peer, network_id, masquerade, metric, enabled, peer_groups, group_peers.peer_id
-	from network_routers, json_each(peer_groups)
+	from network_routers
+	left join json_each(network_routers.peer_groups) on true
 	left join group_peers on group_peers.account_id=? and group_peers.group_id=json_each.value
 	where network_routers.account_id=?
 	`