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>

docs/rules.md

@@ -119,6 +119,10 @@ The action is `accept`, `drop`, `reject` (an ICMP error, or with
 `--reject-with tcp-reset` a TCP reset) or `log` (log and go on).
 `--log` logs the packets of any rule ([operations.md](operations.md#the-log)).
 `--disabled` (or `hc rule disable ID`) keeps a rule without using it.
+`--every-packet` ("every packet" in the web UI) checks a drop or reject
+against every packet, before established connections are accepted, so it
+also stops connections already open, not just new ones; it can't accept
+([operations.md](operations.md#connections)).
 
 Examples: