Rename the go-io import alias from the default `io` to `coreio` in
service.go and config_test.go, matching the alias already used in
config.go. Wrap the bare error return at service.go:48 with
coreerr.E() to include caller context.
Co-Authored-By: Virgil <virgil@lethean.io>
Module path changed from forge.lthn.ai/core/go-config to forge.lthn.ai/core/config.
Package name remains "config" — only the module path changed.
Co-Authored-By: Virgil <virgil@lethean.io>
