feat: task trash, triage trash and retention settings for every area; admin can forbid keeping things for good

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

internal/storage/system.go

@@ -176,6 +176,9 @@ func (s *Store) GetSystemSettings() (*domain.SystemSettings, error) {
 				if n, err := strconv.Atoi(v); err == nil && n > 0 {
 					settings.BackupRetentionDays = n
 				}
+			case "retention_allow_never":
+				allow := v != "false"
+				settings.RetentionAllowNever = &allow
 			}
 		}
 	}
@@ -187,6 +190,10 @@ func (s *Store) GetSystemSettings() (*domain.SystemSettings, error) {
 		}
 	}
 	settings.AllowRegistration = settings.RegistrationMode == RegistrationOpen
+	if settings.RetentionAllowNever == nil {
+		allow := true
+		settings.RetentionAllowNever = &allow
+	}
 	return settings, nil
 }
 
@@ -269,5 +276,9 @@ func (s *Store) UpdateSystemSettings(settings *domain.SystemSettings) error {
 		settings.RegistrationDomains,
 		strconv.FormatBool(settings.RegistrationVerifyEmail),
 	)
+	if err == nil && settings.RetentionAllowNever != nil {
+		_, err = s.db.Exec(`INSERT INTO system_settings (key, value) VALUES ('retention_allow_never', ?)
+			ON CONFLICT(key) DO UPDATE SET value = excluded.value`, strconv.FormatBool(*settings.RetentionAllowNever))
+	}
 	return err
 }