Add MicroStack admin UI with request/resource APIs

[damianh]

Summary

• add a new Blazor WebAssembly admin client (MicroStack.UI.Client) and host (MicroStack.UI) served on a dedicated UI port
• add backend admin APIs for request logging and resource exploration
• implement resource providers for SQS, S3, and DynamoDB to expose names/ARNs and key attributes
• wire solution, container configuration, and docs for dual-port runtime (4566 API + 4567 UI)

Backend changes

• add RequestLog ring buffer + RequestLogMiddleware
• add GET /_microstack/requests and DELETE /_microstack/requests
• add IResourceProvider, ResourceSummary, ResourceItem
• add GET /_microstack/resources
• add MICROSTACK_UI_PORT option and startup logging
• register new AOT JSON types in MicroStackJsonContext

UI changes

• Dashboard page for health/service status/resource counts
• Request Log page with polling, pause/resume, row limits, and clear action
• Resource Explorer page grouped by service
• typed API client with configurable ApiBaseUrl

Validation

• dotnet build src/MicroStack/MicroStack.csproj
• dotnet build src/MicroStack.UI/MicroStack.UI.csproj
• dotnet test tests/MicroStack.Tests/MicroStack.Tests.csproj --filter-not-class MicroStack.Tests.ContainerSmokeTests

Notes

• full solution test restore still hits existing MessagePack vulnerability-as-error failures in Aspire projects
• container smoke test requires Linux NativeAOT toolchain support in the environment