Ban lists: where Guard and fail2ban ban addresses

A program bans an address (every port, or a protocol's ports) for a
time; the ban list says what it is kept from: the firewall, some hosts
behind it, or everything. Bans drop ahead of every rule, close the
address's connections, group IPv6 by /64, are kept in the database
across restarts and audited. Never banned: the inside, the firewall's
own addresses, the caller, the list's never. bans grant (bans:write:LIST),
hc banlist/bans/ban/unban, Traffic -> Bans, a fail2ban action in contrib/,
and failed logins and refused tokens logged for Guard and fail2ban.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/server/server.go

@@ -72,6 +72,8 @@ type Firewall interface {
 	Table(ctx context.Context) (*nft.Table, error)
 	AddElement(ctx context.Context, set, addr string, timeout int) error
 	DeleteElement(ctx context.Context, set, addr string) error
+	AddBan(ctx context.Context, b render.Ban) error
+	DeleteBan(ctx context.Context, b render.Ban) error
 	ListRuleset(ctx context.Context) ([]byte, error)
 	DeleteTable(ctx context.Context, family, name string) error
 	TableText(ctx context.Context, family, name string) (string, error)
@@ -150,6 +152,7 @@ func New(cfg Config, eng *engine.Engine, fw Firewall, ifaces Interfaces, log *sl
 			prev(st)
 		}
 		s.SaveQuotaUsage(context.Background())
+		s.pruneBans(context.Background(), st) // the engine is locked: not s.eng.State()
 	}
 	return s
 }
@@ -324,6 +327,7 @@ func (s *Server) housekeeping(ctx context.Context) {
 				s.log.Warn("purging sessions failed", "err", err)
 			}
 			s.limiter.cleanup()
+			s.pruneBans(ctx, s.eng.State())
 			if s.certs != nil {
 				s.certs.reloadIfChanged()
 			}