feat: OpenAPI metadata extension methods for MapCommand, MapQuery, MapStreamQuery (opt-in and global)

[samtrion]

User Story

As a developer exposing Pulse endpoints via Minimal API, I want OpenAPI metadata (summaries, response types, tags) applied automatically or opt-in to MapCommand, MapQuery, and MapStreamQuery endpoints, so that my Swagger/OpenAPI documentation is accurate without manual configuration per endpoint.

---

Requirements

• Create src/NetEvolve.Pulse.AspNetCore/RouteHandlerBuilderExtensions.cs with opt-in extension methods:
  • WithPulseSummary(): reads
    from XML doc file via XmlDocumentationReader; falls back to type name.
  • WithPulseDescription(string description).
  • WithPulseTag(string tag).
  • WithPulseProduces(): ProducesResponseType(200).
  • WithPulseStreamProduces(): ext/event-stream and �pplication/x-ndjson content types.
• Create src/NetEvolve.Pulse.AspNetCore/Internals/XmlDocumentationReader.cs:
  • Parses *.xml files from assembly output directory.
  • TryGetSummary(Type type, out string? summary) with ConcurrentDictionary cache.
  • No-op (returns
    ull) when XML documentation file absent.
• Create src/NetEvolve.Pulse.AspNetCore/OpenApiMediatorBuilderExtensions.cs:
  csharp public static IMediatorBuilder EnableOpenApiMetadata(this IMediatorBuilder builder)
  Sets OpenApiMetadataEnabled = true via IOptions.
• Update MapCommand, MapQuery, MapStreamQuery in EndpointRouteBuilderExtensions.cs: auto-apply WithPulseSummary() and WithPulseProduces() when OpenApiMetadataEnabled = true.

---

Acceptance Criteria

• WithPulseSummary() returns XML
  text when present; type name as fallback.
• WithPulseProduces() sets correct status code and type.
• EnableOpenApiMetadata() causes auto-application in all three Map* methods.
• XmlDocumentationReader caches results; missing XML file does not throw.
• Unit tests cover all extension methods and XmlDocumentationReader.