Different blocking for different devices: steps and client groups

Client groups put devices (addresses, networks, or ACLs of them) at a
blocking step: off (only your rules), normal (the default), or steps
added above it, each including the lists of the steps below. Lists
start at a step. In each view, a gate policy zone in front of a step's
lists lets the devices below that step through (rpz-client-ip triggers
with rpz-passthru), so every list is still loaded once. The IPv6 part
of a gate leaves the IPv4-mapped range out: named matches IPv4 clients
as ::ffff:a.b.c.d.

Web UI: a Devices panel on the Blocking page and a step on each list.
CLI: jarl block step, jarl block group, jarl blocklist --step. API:
/blocking/steps, /blocking/groups. Database schema 8.

Also: copying the state kept empty lists as empty (not nil), so
reverting a changeset no longer adds restore operations for unchanged
blocklists, rules and views.

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

docs/cli.md

@@ -476,6 +476,12 @@ jarl block delete DOMAIN [--view V] | --id ID
 jarl block check DOMAIN                          # blocked? by which rule or list?
 jarl block pause [DURATION]                      # let everything through for a while (default 10m, at most 24h)
 jarl block pause indefinitely                    # ... until 'jarl block resume'
+jarl block step list | add NAME | rename STEP NEW | order STEP... | delete STEP
+jarl block group list
+jarl block group add NAME MEMBER... [--step S] [--view V]...   # addresses, networks or ACLs
+jarl block group update GROUP [--add M] [--remove M] [--step S] [--name N]
+jarl block group delete GROUP
+jarl blocklist update LIST --step STEP           # devices at that step or above get it
 jarl block resume
 ```