Shared backend library
This is a Go library module, not an executable. It provides database connections, transactions and repository primitives, errors, structured logging, generic HTTP responses, configuration and rate-limit helpers. It contains no customer, session, verification or Sendico domain models and imports no executable SXCHNGE module.
product consumes it through a local module replacement. A future backoffice
executable can consume the same infrastructure independently.
Run go test -race ./... and go vet ./... here, or use the root Make targets to
validate all implemented backend modules.