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>

internal/config/presets.go

@@ -0,0 +1,36 @@
+package config
+
+import (
+	_ "embed"
+	"sync"
+
+	"go.yaml.in/yaml/v3"
+)
+
+//go:embed presets.yaml
+var presetsYAML []byte
+
+// Preset is a built-in watch: patterns, and where the lines usually are.
+type Preset struct {
+	Description string   `yaml:"description"`
+	File        string   `yaml:"file"`
+	Journal     *Journal `yaml:"journal"`
+	Source      string   `yaml:"source"`
+	Match       []string `yaml:"match"`
+	Ignore      []string `yaml:"ignore"`
+}
+
+// Presets are the built-in presets by name.
+var Presets = sync.OnceValue(func() map[string]Preset {
+	out := map[string]Preset{}
+	if err := yaml.Unmarshal(presetsYAML, &out); err != nil {
+		panic("presets.yaml: " + err.Error())
+	}
+	return out
+})
+
+//go:embed example.yaml
+var exampleYAML []byte
+
+// Example is a commented configuration (guard config --example).
+func Example() string { return string(exampleYAML) }