Implement distributed tracing across edge functions:
- Introduce span types and utilities (logger.ts enhancements)
- Replace request tracking with span-based tracing in approval and rejection flows
- Propagate and manage W3C trace context in edge tracking
- Add span visualization scaffolding (spanVisualizer.ts) and admin TraceViewer UI (TraceViewer.tsx)
- Create tracing-related type definitions and support files
- Prepare RPC call logging with span context and retries
