turbopuffer REST API

Single REST API for all turbopuffer operations — namespace metadata, write (upsert / patch / delete), vector ANN query, full-text BM25 query, hybrid query, multi-query, explain_query, branch_from, copy_from, and cache warming — with bearer-token authentication. The base host is region-templated as https://{region}.turbopuffer.com (e.g., gcp-us-east4.turbopuffer.com or aws-us-east-1.turbopuffer.com) to minimize egress and latency.