Add Wolverine.HealthChecks for ASP.NET Core IHealthCheck integration (CritterWatch#73)

[jeremydmiller]

Summary

Adds a new thin extension package, WolverineFx.HealthChecks, that plugs Wolverine into the standard ASP.NET Core
health-check pipeline. Two checks ship in the box:

• WolverineBusHealthCheck — Healthy when the runtime has finished starting and the runtime cancellation token has not been signalled. HealthCheckResult.Data exposes serviceName, uniqueNodeId, started, cancellationRequested.
• WolverineListenerHealthCheck — Walks IWolverineRuntime.Endpoints.ActiveListeners() and reports:
  • Healthy — all listeners Accepting
  • Degraded — any listener TooBusy or GloballyLatched
  • Unhealthy — all listeners Stopped
  • Per-listener counts and a URI-keyed status map go into HealthCheckResult.Data so dashboards can render detail without a second probe.

API shape

Conventional IHealthChecksBuilder extensions (mirrors Microsoft.Extensions.Diagnostics.HealthChecks + community packages):

builder.Services.AddHealthChecks()
    .AddWolverine(tags: new[] { "live", "ready" })
    .AddWolverineListeners(
        filter: agent => agent.Uri.Scheme == "rabbitmq",
        tags: new[] { "ready" });

Both extensions accept name / failureStatus / tags / timeout. AddWolverineListeners also takes an optional Func<IListeningAgent, bool> filter for scoping a check to a subset of listeners — useful when you want a separate readiness probe per transport.

Out of scope

Per-broker connectivity health checks (RabbitMQ, Azure Service Bus, Kafka, etc.) are deliberately not part of this PR — they live with each transport package and will be addressed by transport-specific helpers (tracked separately under CritterWatch#70).

Implementation notes

• New project lives at src/Wolverine.HealthChecks/. It depends only on Wolverine core + Microsoft.Extensions.Diagnostics.HealthChecks(.Abstractions). Microsoft.Extensions.* health-check packages are real dependencies, so we did not fold these checks into Wolverine.Http where they would weigh down every Wolverine.Http consumer.
• Versions are centrally managed in Directory.Packages.props against the existing TFM-conditional Microsoft.Extensions.* version ranges.
• The new project + tests project are added to wolverine.slnx. wolverine_slim.slnx is unchanged.
• Docs page added at docs/guide/health-checks.md and wired into the VitePress sidebar next to the existing Diagnostics page.

Test plan

• Unit tests against an IWolverineRuntime substitute cover started / not-started / cancellation-requested for the bus check, and Healthy / Degraded / Unhealthy / scope-filter cases for the listener check (NSubstitute, already a dev dependency).
• Integration test boots an in-process Microsoft.AspNetCore.TestHost host with .AddWolverine().AddWolverineListeners() and asserts /health, /health/live, /health/ready all return 200.
• dotnet build wolverine.slnx — clean (0 errors).
• dotnet test src/Wolverine.HealthChecks.Tests/Wolverine.HealthChecks.Tests.csproj — 13/13 passing.

Refs CritterWatch#73.