docs(health): align shared-contract to shipped API + per-lib CLAUDE.md + cleanup

- Contract: DatabaseHealthCheck<TContext> ctor now shows IServiceProvider (resolves
  IDbContextFactory<TContext> when registered, else a scoped TContext; pool-safe)
- Contract: RequireActiveNode gains retryAfterSeconds = 5 default parameter
- Packages: remove dangling AspNetCore.HealthChecks.UI.Client PackageVersion (no
  csproj referenced it)
- Tests: fix CS8625 in RoleLessCases — use object?[] so null role rows compile
  warning-free under Nullable=enable
- Add ZB.MOM.WW.Health/CLAUDE.md (packages, responsibilities, consumer matrix,
  build/test/pack commands, status + pointer to components/health/)

components/health/shared-contract/ZB.MOM.WW.Health.md

@@ -91,7 +91,8 @@ public interface IActiveNodeGate
 public static class ActiveNodeGateExtensions
 {
     public static IEndpointConventionBuilder RequireActiveNode(
-        this IEndpointConventionBuilder builder);
+        this IEndpointConventionBuilder builder,
+        int retryAfterSeconds = 5);
 }
 
 /// Checks that a downstream gRPC channel is reachable.
@@ -221,8 +222,9 @@ namespace ZB.MOM.WW.Health.EntityFrameworkCore;
 public sealed class DatabaseHealthCheck<TContext> : IHealthCheck
     where TContext : DbContext
 {
+    // Resolves IDbContextFactory<TContext> when registered, else a scoped TContext; pool-safe.
     public DatabaseHealthCheck(
-        IDbContextFactory<TContext>      factory,
+        IServiceProvider                      serviceProvider,
         DatabaseHealthCheckOptions<TContext>? options = null);
 
     public Task<HealthCheckResult> CheckHealthAsync(