feat: add frontend system health diagnostics and mute HF Celery gossip

feat: implement backend ingestion pipeline with Celery workers, Qdrant integration, and session management

feat: implement backend candidate matching pipeline with Pinecone integration, FastAPI routers, and ingestion workers.

feat: stabilize celery loops, add redis caching, and scale stage 2 neural limit to 250

feat: implement session-based candidate matching architecture

feat: implement feature builder with growth velocity and JD quality scoring