DLP: how long held mail waits is a setting

inbuxa:DlpSettings (singleton, urn:inbuxa:jmap): keepHeldDays, 1 to 90,
7 by default (settled answer 5 made it a setting). sysDlpPolicyGet reads
it, sysDlpPolicyUpdate changes it, server-level, audited by the request
layer. Each held message keeps the days it was given, and the sender's
notices say that number. Privacy catalog entry; spec §2.6 updated.

mail_rules_tests: 7 by default, 0 refused, 3 set and a message held
afterwards expires 3 days after it was held, the expiry notice says 3.

crates/jmap-proto/src/references/resolve.rs

@@ -47,6 +47,7 @@ impl Response<'_> {
                 GetRequestMethod::DeletedAccount(request) => request.resolve_references(self)?,
                 GetRequestMethod::AiLimits(request) => request.resolve_references(self)?,
                 GetRequestMethod::LogSettings(request) => request.resolve_references(self)?,
+                GetRequestMethod::DlpSettings(request) => request.resolve_references(self)?,
                 GetRequestMethod::DataInventory(request) => request.resolve_references(self)?,
                 GetRequestMethod::InventorySnapshot(request) => request.resolve_references(self)?,
                 GetRequestMethod::AuditEvent(request) => request.resolve_references(self)?,
@@ -106,6 +107,9 @@ impl Response<'_> {
                 SetRequestMethod::LogSettings(request) => {
                     request.resolve_references(self, 1, false)?
                 }
+                SetRequestMethod::DlpSettings(request) => {
+                    request.resolve_references(self, 1, false)?
+                }
                 SetRequestMethod::Explanation(request) => {
                     request.resolve_references(self, 1, false)?
                 }