feat: implement self-healing online model retraining loop on statistical data drift detection

fix(backend): remove undefined client reference in FastAPI shutdown handler

feat: migrate and consolidate all operational logging, structured tracing, and metrics to Supabase PostgreSQL, removing MongoDB Atlas dependency

feat: make backend resilient against PostgreSQL pool initialization crashes on startup

feat: complete NeuralVault 3.0 hardening including AST parameterization fix, KS data drift, Cross-Encoder, and Docker Compose

feat: NeuralVault 2.0 - Complete Free-Tier Groq & ML Explainability Architecture