M2 data path: BSD netisr workqueue + lock reentrancy fixes + diagnostics

- hooks: packets are queued to pfk_netisr ordered wq (process context) and
  re-injected with an skb->mark guard (PFK_MARK_PASSED); softirq-safe,
  documented divergence vs OpenBSD in-place ip_input continuation
- pfk_rwlock: per-task writer recursion (NET/PF lock nesting like OpenBSD)
- pfk_net: holder-task+depth reentrancy (pid-based hack removed)
- ifnet events deferred to ordered workqueue (rtnl AB-BA fix)
- idr iteration start index fix (kifs were never attached -> kif==NULL drop)
- pfk_lock_trace module param for lock diagnostics
- tests/vm: 01-state 02-block 03-tables 04-anchors + lib; vm-run-tests.sh
- docs/en/install.md: apply/build guide (core patch set currently EMPTY)

tests/vm/02-block.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+# M2 gate 2: block drop + block return-rst verified at packet level
+set -uo pipefail; cd "$(dirname "$0")"; . ./lib.sh
+pf0 '/opt/pf/pfctl -e; /opt/pf/pfctl -f /dev/null' >/dev/null
+pf0 'echo "block drop in quick proto icmp from any to any
+pass out quick" | /opt/pf/pfctl -f -'
+cli "ping -c 2 -W 1 $SRV_IP >/dev/null 2>&1" && bad "icmp still passes" || ok "icmp blocked"
+# return-rst on tcp: cli nc to closed-filtered port expects RST back
+pf0 'echo "block return-rst in quick proto tcp from any to any port 8080
+pass out quick" | /opt/pf/pfctl -f -'
+srv 'timeout 3 nc -l -p 8080 >/dev/null 2>&1 &' ; sleep 0
+cli 'timeout 3 nc -z 10.0.2.20 8080; echo NC=$?' | grep -q 'NC=1' && ok "tcp refused (rst)" || bad "tcp not refused"
+pf0 '/opt/pf/pfctl -d' >/dev/null; finish