fix(health): bump to ZB.MOM.WW.Health 0.2.1 — Traefik leader-pinning now works

0.2.1 makes the shared ActiveNodeHealthCheck return Unhealthy (503), not
Degraded (200), for a node that carries the role but is not the role leader.
That is what the shared health spec always specified, what docs/ServiceHosting.md,
docs/v2/Architecture-v2.md and the 2026-05-26 alignment design all describe
("200 only on the Admin-role leader; 503 elsewhere"), and what
docker-dev/traefik-dynamic.yml + scripts/install/traefik-dynamic.yml assume when
they use /health/active as the load-balancer probe.

The implementation returned Degraded, which MapZbHealth maps to 200, so BOTH
central nodes always passed the probe and Traefik load-balanced the admin UI
across the pair instead of pinning it to the leader. The docs were right; the
code was wrong. Closes the Traefik half of #494.

No OtOpcUa code change — package pin only.

Live-verified on docker-dev, with the MAIN pair genuinely formed (memberCount 2,
both members naming one leader):

  central-1 (leader)  /health/active -> 200   traefik UP
  central-2 (standby) /health/active -> 503   traefik DOWN

Failover drill (README step 2), which had never actually exercised anything:
stopping central-1 flipped Traefik to central-2 within 20 s and
http://localhost:9200/ answered 200 continuously across the swap — no outage.
Restarting central-1 reclaimed the role-leader and Traefik flipped back.

README corrected on two counts: the drill now states that exactly ONE backend is
UP by design, and step 3 no longer claims central-2 keeps leadership — RoleLeader
is the lowest-address member, so central-1 deterministically reclaims it. Added
the cold-boot caveat that starting both nodes at once can leave each self-forming
a 1-member cluster, in which case both are their own leader and both answer 200.

STILL OPEN in #494: driver-only nodes. The check is scoped to the admin role and
returns Healthy for any node that lacks it, so all four site nodes answer 200 and
the real per-Cluster redundancy Primary (oldest Up driver member, IsDriverPrimary)
is still not what this tier reports.

Directory.Packages.props

@@ -140,7 +140,7 @@
     <PackageVersion Include="xunit" Version="2.9.3" />
     <PackageVersion Include="xunit.runner.visualstudio" Version="3.0.2" />
     <PackageVersion Include="xunit.v3" Version="1.1.0" />
-    <PackageVersion Include="ZB.MOM.WW.Health" Version="0.2.0" />
+    <PackageVersion Include="ZB.MOM.WW.Health" Version="0.2.1" />
     <!--
       LocalDb: embedded SQLite node-local cache + optional 2-node gRPC replication. The core
       package floors the native SQLitePCLRaw.lib.e_sqlite3 at 2.1.12, so consumers inherit the
@@ -148,8 +148,8 @@
     -->
     <PackageVersion Include="ZB.MOM.WW.LocalDb" Version="0.1.3" />
     <PackageVersion Include="ZB.MOM.WW.LocalDb.Replication" Version="0.1.3" />
-    <PackageVersion Include="ZB.MOM.WW.Health.Akka" Version="0.2.0" />
-    <PackageVersion Include="ZB.MOM.WW.Health.EntityFrameworkCore" Version="0.2.0" />
+    <PackageVersion Include="ZB.MOM.WW.Health.Akka" Version="0.2.1" />
+    <PackageVersion Include="ZB.MOM.WW.Health.EntityFrameworkCore" Version="0.2.1" />
     <PackageVersion Include="ZB.MOM.WW.Telemetry" Version="0.1.0" />
     <PackageVersion Include="ZB.MOM.WW.Telemetry.Serilog" Version="0.1.0" />
     <PackageVersion Include="ZB.MOM.WW.MxGateway.Client" Version="0.1.1" />