feat(security): apikey --expires CLI flag + dashboard expiry/staleness badge (SEC-10 polish)

Gateway-side follow-up to the shared auth-lib expiry core (delivered via G-2):

- apikey create-key gains optional --expires — absolute ISO-8601 UTC or relative
  <N>d/<N>h from now; omitted means non-expiring (opt-in, unchanged default).
  Threaded ApiKeyAdminCommand -> parser -> runner into the library's
  CreateKeyAsync(..., expiresUtc, ...). list-keys shows an expiry column and an
  active/expired/revoked status.
- Dashboard API Keys page surfaces expiry: an Expires column (Never when unset)
  and a status badge reading Expired (red) / Expiring (<=7d, amber) / Revoked /
  Active. DashboardApiKeySummary.ExpiresUtc projected in DashboardSnapshotService;
  StatusBadge maps the new states.

Tests: parser (absolute/relative/invalid/none) + end-to-end past-expiry rejection
through the live verifier; dashboard summary suite green. Docs: Authentication.md
(verification-flow expiry step, CLI table + examples, dashboard badge).

Closes the tracked SEC-10 polish (SEC-10 core was already Done).

src/ZB.MOM.WW.MxGateway.Server/Dashboard/DashboardSnapshotService.cs

@@ -273,7 +273,8 @@ public sealed class DashboardSnapshotService : IDashboardSnapshotService
                     Constraints: ApiKeyConstraintSerializer.Deserialize(key.ConstraintsJson),
                     CreatedUtc: key.CreatedUtc,
                     LastUsedUtc: key.LastUsedUtc,
-                    RevokedUtc: key.RevokedUtc))
+                    RevokedUtc: key.RevokedUtc,
+                    ExpiresUtc: key.ExpiresUtc))
                 .ToArray();
 
             Volatile.Write(ref _apiKeySummaries, summaries);