feat(gateway): implement IntelligenceClient HTTP integration

[rsalus]

Note for implementers: The design outlined here is a guideline, not a strict specification. Feel free to pivot from the suggested approach if you discover a better solution during implementation. Update the issue with your rationale when deviating significantly.

Summary

Replace the stub IntelligenceClient with production HTTP calls to the Intelligence service /analyze endpoint.

Context

The current implementation returns hardcoded mock data. Production implementation must:

1. Serialize ClinicalBundle to JSON
2. POST to /analyze endpoint with timeout handling
3. Deserialize response to PAFormData
4. Handle errors gracefully

Dependencies

Issue	Relationship
#9	Blocked by - data contracts must be stable

Tasks

Core Implementation

• Inject HttpClient via IHttpClientFactory
• Serialize ClinicalBundle to JSON
• POST to {BaseUrl}/analyze
• Deserialize response to PAFormData

Resilience (Polly)

• Retry policy (exponential backoff, max 3)
• Circuit breaker (threshold: 5, 30s break)
• Timeout policy (30s default)

Error Handling

• Handle HttpRequestException
• Handle timeout scenarios
• Handle non-2xx status codes
• Log errors with correlation ID

Testing

• Unit tests with mocked HttpMessageHandler
• Test retry and circuit breaker behavior

Files

File	Action
apps/gateway/Gateway.API/Services/IntelligenceClient.cs	Modify
apps/gateway/Gateway.API/Configuration/IntelligenceOptions.cs	Reference
apps/gateway/Gateway.API.Tests/Services/IntelligenceClientTests.cs	Create

Design References

• §2.1 Gateway Service
• §6.2 Timeout Management