feat(health): 0.2.0 — optional per-entry data + Akka cluster-view

Phase 0 of docs/plans/2026-07-22-overview-dashboard-impl-plan.md: give the
canonical health JSON a structured channel so the family overview dashboard can
read each Akka cluster's current leader.

- ZbHealthWriter: optional `"data": {...}` per entry, sourced from
  HealthReportEntry.Data, emitted only when non-empty. Per-property JsonIgnore
  (NOT a global DefaultIgnoreCondition) so `"description": null` still renders —
  payloads from data-less checks stay byte-identical to 0.1.0.
- AkkaClusterHealthCheck: BuildClusterData publishes this node's own view —
  leader (omitted while unknown), selfAddress, selfRoles (sorted), memberCount,
  unreachableCount — on every result path. The startup-safety paths (no
  ActorSystem / cluster inaccessible) stay description-only.
- Tests: writer data emit/omit (raw-JSON assert on the omit case), and a real
  single-node self-joined cluster via Akka.TestKit.Xunit2 for the data values.
  70 tests green (25/39/6).
- Version 0.1.0 -> 0.2.0; 3 packages published to the Gitea feed and
  restore-verified from a scratch consumer, which serves data.leader live.

ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Akka.Tests/AkkaClusterStatusPolicyTests.cs

@@ -88,6 +88,8 @@ public sealed class AkkaClusterStatusPolicyTests
             var result = await check.CheckHealthAsync(NewContext(check));
 
             Assert.Equal(HealthStatus.Degraded, result.Status);
+            // No cluster to describe → no data, so the emitted payload stays the pre-0.2.0 shape.
+            Assert.Empty(result.Data);
         }
         finally
         {