feat: PulseGrpcStreamService and MapStreamQueryGrpc() for gRPC server-streaming (Low Priority)

[samtrion]

User Story

As a developer exposing Pulse stream queries over gRPC, I want PulseGrpcStreamService and MapStreamQueryGrpc(), so that gRPC clients can consume IMediator.StreamQueryAsync results via server-streaming RPCs.

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Background

⚠️ Low priority — implement only after all Tier 1–5 items are complete.

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Requirements

• Create src/NetEvolve.Pulse.AspNetCore/Grpc/PulseGrpcStreamService.cs:
  • �bstract class PulseGrpcStreamService<TQuery, TResponse> that writes to IServerStreamWriter by iterating IMediator.StreamQueryAsync.
  • Concrete subclasses define Protobuf mapping.
• Add MapStreamQueryGrpc<TQuery, TResponse>(this IEndpointRouteBuilder) extension method.
• Unit tests for service and extension method.

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Acceptance Criteria

• Service writes all stream items to IServerStreamWriter.
• Client cancellation stops the stream.
• MapStreamQueryGrpc() registers the gRPC service correctly.
• Unit tests pass.