Guard: watch logs, ban misbehaving addresses in Housecarl

Files and the journal, patterns with one <IP>, bounties within a window,
bans in a Housecarl ban list with repeat offenders' bans growing; presets
for sshd, jarl, housecarl, steward, bind-xfr, postfix-sasl, dovecot,
nginx-auth and housecarl-drops; guard run/check/test/status/bans/ban/unban;
a Debian package with a sandboxed unit; an end-to-end test with Housecarl.

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

testdata/presets/nginx-auth.txt

@@ -0,0 +1,3 @@
+203.0.113.9	2026/10/22 10:00:00 [error] 1234#1234: *5 user "admin" was not found in "/etc/nginx/.htpasswd", client: 203.0.113.9, server: example.com, request: "GET / HTTP/1.1", host: "example.com"
+203.0.113.9	2026/10/22 10:00:00 [error] 1234#1234: *5 user "adam": password mismatch, client: 203.0.113.9, server: example.com, request: "GET / HTTP/1.1"
+-	2026/10/22 10:00:00 [error] 1234#1234: *5 open() "/var/www/favicon.ico" failed (2: No such file or directory), client: 203.0.113.9, server: example.com