Journaling: capture at the queue, the built-in journal, retention

Phase 2 of the journaling spec.

- A copy of each message is taken in MessageWrapper::queue, after DLP and
  transport rules, for every enabled journal that takes it (direction and
  scope: everyone, or accounts, groups, domains, tenants). If the copy
  can't be taken the message isn't queued (temporary failure).
- The journal report: the envelope one field a line (sender, To, Cc, Bcc
  from the envelope, list members from their ORCPT, direction, held for
  review), then the queued message byte for byte as message/rfc822.
- The built-in journal under J in the inbuxa subspace: one chain per node
  whose links name each entry by SHA-256, so entries can expire out of
  chain order; purge leaves a marker, and verify catches an entry changed
  or removed early and a report that doesn't match.
- Retention per journal (30 to 3650 days); an entry keeps what it was
  written with. The daily maintenance purges what's due, keeping entries
  whose people a legal hold covers (deleted accounts a hold keeps too),
  and records the counts in the audit log.
- inbuxa:Journal get/set, audited by the request layer. Permissions
  680-683: administrators see and change journals; the Compliance Officer
  sees, searches and exports. Whoever changes journals may grant search and
  export without holding them, so officers can still be appointed.
- Catalog entries (inbuxa:Journal, source "journal"); spec as-built notes.

tests/src/system/journal.rs: validation, internal mail with a Bcc,
outgoing into two journals, incoming over LMTP, the report and its
original, tamper and early removal caught, hold-aware purge, retention
changes leave entries alone, disabled and removed journals take nothing.

crates/common/src/auth/permissions.rs

@@ -165,6 +165,14 @@ impl AccessToken {
         mut requested_permissions: Permissions,
     ) -> Result<(), Vec<Permission>> {
         requested_permissions.difference(self.permissions_bits());
+        // inbuxa: journaling, JR-18: whoever sets up journals may give
+        // others (or, through a role, themselves) the reading of them,
+        // which administrators don't hold by default; the role change is
+        // in the audit log
+        if self.has_permission(Permission::SysJournalUpdate) {
+            requested_permissions.clear(Permission::SysJournalSearch as usize);
+            requested_permissions.clear(Permission::SysJournalExport as usize);
+        }
         if requested_permissions.is_empty() {
             Ok(())
         } else {
@@ -307,6 +315,13 @@ impl Default for DefaultPermissions {
                 | Permission::SysDlpReviewUpdate => {
                     default.superuser.push(permission);
                 }
+                // inbuxa: journals are the server's; administrators set them
+                // up but read what's journaled only if granted it
+                // (journaling spec, JR-18, settled answer 5)
+                Permission::SysJournalGet | Permission::SysJournalUpdate => {
+                    default.superuser.push(permission);
+                }
+                Permission::SysJournalSearch | Permission::SysJournalExport => {}
                 // inbuxa: AL-12: tenant administrators lock and delegate
                 // within their tenant
                 Permission::SysAccountLockGet