feat(12.2-01): add deferred:purge, its daily framework schedule and relation child hooks

- deferred:purge [--days] in lagoon.RuntimeCommands (purge_days, default 5)
- lagoon.FrameworkSchedule entry at purge_at (default 03:00, empty disables)
- conga prepends framework entries as summercms.lagoon[i]:<command>
- pact.Relation{Before,After}{Create,Update,Delete} optional hooks
- lagoon, conga and pact READMEs, scheduling and setup docs

modules/lagoon/schedule.go

@@ -0,0 +1,58 @@
+package lagoon
+
+import (
+	"fmt"
+	"regexp"
+	"strconv"
+	"strings"
+
+	"git.golem15.com/golem15/summercms/modules/backpack"
+	"git.golem15.com/golem15/summercms/modules/pact"
+)
+
+// FrameworkScheduleID is the plugin id under which the scheduler lists the
+// framework's own schedule entries, so the daily purge has the entry id
+// summercms.lagoon[0]:deferred:purge.
+const FrameworkScheduleID = "summercms.lagoon"
+
+const (
+	purgeAtKey     = "database.deferred_bindings.purge_at"
+	purgeDaysKey   = "database.deferred_bindings.purge_days"
+	defaultPurgeAt = "03:00"
+	// defaultPurgeDays is WinterCMS's DeferredBinding::cleanUp(5).
+	defaultPurgeDays = 5
+)
+
+var purgeAtPattern = regexp.MustCompile(`^([01][0-9]|2[0-3]):([0-5][0-9])$`)
+
+// FrameworkSchedule returns the scheduled commands the framework itself
+// runs: deferred:purge daily at database.deferred_bindings.purge_at ("HH:MM"
+// in app.timezone, default "03:00"). An explicitly empty purge_at disables
+// the entry; a malformed one is an error naming the key. A nil app or an app
+// without config returns no entries and no error.
+func FrameworkSchedule(app *backpack.App) ([]pact.ScheduledCommand, error) {
+	if app == nil || app.Config == nil {
+		return nil, nil
+	}
+	at := defaultPurgeAt
+	if raw, ok := app.Config.Lookup(purgeAtKey); ok {
+		switch v := raw.(type) {
+		case nil:
+			at = ""
+		case string:
+			at = strings.TrimSpace(v)
+		default:
+			return nil, fmt.Errorf("lagoon: %s must be a quoted \"HH:MM\" string, got %v", purgeAtKey, raw)
+		}
+	}
+	if at == "" {
+		return nil, nil
+	}
+	m := purgeAtPattern.FindStringSubmatch(at)
+	if m == nil {
+		return nil, fmt.Errorf("lagoon: %s %q is not HH:MM (00:00 to 23:59)", purgeAtKey, at)
+	}
+	hour, _ := strconv.Atoi(m[1])
+	minute, _ := strconv.Atoi(m[2])
+	return []pact.ScheduledCommand{{Command: "deferred:purge", Cadence: pact.DailyAt(hour, minute)}}, nil
+}