refactor: remove Azure OpenTelemetry integration and implement core RAG pipeline orchestration with backend setup

Fix: Add mandatory service.name to OTEL Resource for Azure Ingestion

Diag: Use manual AzureMonitorTraceExporter for lower-level control and debug

Diag: Add manual test span to /api/diag for connectivity verification

Fix: Restore main.py logic and switch to direct uvicorn for tracing stability

Diag: Add /api/diag endpoint and improved Azure Monitor initialization logic

Fix: Improve Azure Monitor initialization and robust connection string parsing

Feat: Add Azure AI Foundry Tracing and update documentation

Fix: Graceful error handling - never show blank responses on errors

Fresh cleaner push without any mp4