add logfire opentelemetry instrumentation
- replace env_logger with logfire for structured observability
- add opentelemetry middleware for automatic http request tracing
- instrument search operations with custom spans:
- embedding generation
- vector search
- bm25 search
- reciprocal rank fusion
- remove unused upsert method and struct from turbopuffer client
(ingestion script calls api directly, not used by main application)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>