Connections, "every packet" rules, and a packet tracer

- Connections: the kernel's tracked connections, read and closed over
  ctnetlink (internal/conntrack, raw netlink like the drop log), with
  their NAT and TCP state; closing one makes the rules check its next
  packet again (GET /connections, POST /connections/close; hc
  connections; Traffic → Connections).
- Rules can check every packet (every_packet, --every-packet): before
  established connections are accepted, so a drop or reject also stops
  connections already open. They can't accept.
- A packet tracer (internal/trace): a table of its own, inet
  housecarl-trace, marks the packets a filter picks, `nft monitor trace`
  reports every rule and policy they meet in every table, and the tracer
  names what accepted or dropped them, Housecarl's rules by name (POST,
  GET, DELETE /trace; hc trace; Traffic → Trace). One trace at a time,
  at most 200 packets and 20 a second; the table goes when it ends.

e2e: 157 checks, among them an upload a normal block doesn't stop and an
every-packet one does, and a trace naming the blocking rule.

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

internal/validate/validate_test.go

@@ -104,6 +104,7 @@ func TestCodes(t *testing.T) {
 		{"rule_quota_reset", func(st *model.State) { rule(st).Quota = &model.Quota{Bytes: 1, Reset: "daily", Day: 3} }},
 		{"rule_group", func(st *model.State) { rule(st).GroupV6 = 129 }},
 		{"rule_traffic_accept", func(st *model.State) { rule(st).Quota = &model.Quota{Bytes: 1 << 20} }},
+		{"rule_every_packet_accept", func(st *model.State) { rule(st).EveryPacket = true }},
 		{"flowtable_traffic", func(st *model.State) {
 			st.Settings.FlowtableDevices = []string{"wan"}
 			st.Rules[1].Action, st.Rules[1].Quota = model.ActionDrop, &model.Quota{Bytes: 1 << 20, Over: true}