Orchestrator fan out logic implemented

[yoonseo-han]

🧠 Summary

Explain what this PR does.

Implemented a Parallel Fan-out Retriever Architecture to improve system throughput and fault tolerance. The Orchestrator now queries all domain-specific retrievers (proj_spec, tech_concept, dev_log, ops_ts) concurrently instead of using a single-domain routing logic.

🧩 Related Issues

Closes #37

🧰 Changes

• Feature / Improvement
• Bug Fix
• Test (Unit / Integration)
• Refactor / Cleanup
• Documentation

🧪 Development Notes

Use this section to help reviewers understand the implementation.

• Asynchronous Parallelism: Migrated from synchronous requests to httpx.AsyncClient with asyncio.gather for non-blocking I/O.
• Fault Tolerance: Enabled return_exceptions=True in the gather call to ensure Graceful Degradation. Even if one retriever fails or times out, the system continues to generate answers using data from the remaining healthy nodes.
• Global Re-ranking: Introduced a score-based sorting mechanism to merge and prioritize context results from multiple domains before sending them to the Generator.

🔍 Testing

Describe how you tested the change.

• Parallel Execution Test: Verified through logs that all four retriever requests are triggered simultaneously.
• Partial Failure Test: Manually stopped the ops_ts container and confirmed that the Orchestrator still provides answers based on other available domains.

🚀 Deployment Notes

Any special considerations for deployment