fix(host): resolve Host-001 — exclude leader-only active-node check from /health/ready

src/ScadaLink.Host/Program.cs

@@ -131,9 +131,14 @@ try
         app.UseAuthorization();
         app.UseAntiforgery();
 
-        // WP-12: Map readiness endpoint — returns 503 until all checks pass, 200 when ready
+        // WP-12: Map readiness endpoint — returns 503 until ready, 200 when ready.
+        // REQ-HOST-4a defines readiness as cluster membership + DB connectivity,
+        // explicitly NOT cluster leadership. The leader-only "active-node" check is
+        // excluded here so a fully operational standby central node reports ready;
+        // leadership is reported separately on /health/active.
         app.MapHealthChecks("/health/ready", new HealthCheckOptions
         {
+            Predicate = check => check.Name != "active-node",
             ResponseWriter = UIResponseWriter.WriteHealthCheckUIResponse
         });