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.

docs/plans/2026-07-22-overview-dashboard-impl-plan.md.tasks.json

@@ -0,0 +1,25 @@
+{
+  "plan": "docs/plans/2026-07-22-overview-dashboard-impl-plan.md",
+  "tasks": [
+    { "id": "1",  "subject": "0.1 Health writer: optional per-entry `data` object", "status": "pending", "blockedBy": [] },
+    { "id": "2",  "subject": "0.2 AkkaClusterHealthCheck: populate cluster-view data", "status": "pending", "blockedBy": [] },
+    { "id": "3",  "subject": "0.3 Health 0.2.0: version, test, pack, publish, verify", "status": "pending", "blockedBy": ["1", "2"] },
+    { "id": "4",  "subject": "1.1 ScadaBridge: bump Health packages to 0.2.0", "status": "pending", "blockedBy": ["3"] },
+    { "id": "5",  "subject": "1.2 ScadaBridge: site health checks (akka-cluster, localdb, active-node)", "status": "pending", "blockedBy": ["4"] },
+    { "id": "6",  "subject": "1.3 ScadaBridge: map MapZbHealth on the site pipeline", "status": "pending", "blockedBy": ["5"] },
+    { "id": "7",  "subject": "1.4 ScadaBridge: site health tests", "status": "pending", "blockedBy": ["6"] },
+    { "id": "8",  "subject": "2.1 OtOpcUa: verify `akka` check is the shared AkkaClusterHealthCheck", "status": "pending", "blockedBy": [] },
+    { "id": "9",  "subject": "2.2 OtOpcUa: bump Health to 0.2.0", "status": "pending", "blockedBy": ["3", "8"] },
+    { "id": "10", "subject": "2.3 Alignment bumps: mxgw + HistorianGateway Health 0.2.0", "status": "pending", "blockedBy": ["3"] },
+    { "id": "11", "subject": "3.1 Overview: scaffold project", "status": "pending", "blockedBy": ["3"] },
+    { "id": "12", "subject": "3.2 Overview: registry options + validation", "status": "pending", "blockedBy": ["11"] },
+    { "id": "13", "subject": "3.3 Overview: health client + status model", "status": "pending", "blockedBy": ["11"] },
+    { "id": "14", "subject": "3.4 Overview: poller + snapshot store", "status": "pending", "blockedBy": ["12", "13"] },
+    { "id": "15", "subject": "3.5 Overview: leader aggregation", "status": "pending", "blockedBy": ["13"] },
+    { "id": "16", "subject": "3.6 Overview: UI (ThemeShell, Overview page, InstanceCard)", "status": "pending", "blockedBy": ["14", "15"] },
+    { "id": "17", "subject": "3.7 Overview: self-observability", "status": "pending", "blockedBy": ["14"] },
+    { "id": "18", "subject": "3.8 Overview: tests", "status": "pending", "blockedBy": ["16", "17"] },
+    { "id": "19", "subject": "3.9 Overview: config + docker", "status": "pending", "blockedBy": ["17"] },
+    { "id": "20", "subject": "4 Live acceptance (design §9)", "status": "pending", "blockedBy": ["7", "9", "18", "19"] }
+  ]
+}