v1.3.0 — Email stock API

Adds Client.GetEmailStock(ctx, appName, emailType) and EmailStockResponse for the REGHelp GET /email/getStock API. Read available addresses by application (tg, ig, wa) without creating a task, reserving an address or charging balance.

Responses include canonical AppName, nonnegative Count, UTC UpdatedAt, Service and Status. Invalid or incomplete responses are rejected. Disabled services return ErrServiceDisabled; UPSTREAM_ERROR is recognized by errors.Is(err, ErrExternalService) while preserving the server error code.

Updated English/Russian README examples, changelog and default User-Agent version. Existing methods remain compatible.

Validation: go test ./... -race -count=1, go vet ./... and go build ./... passed.

go get github.com/REGHELPNET/reghelp-client-go@v1.3.0