feat(valid): initial stable release v0.9.0

Struct validation backed by go-playground/validator/v10 with xerrors integration and pluggable i18n message providers.

What's included:
- Validator interface with Struct(v any) error method
- New(...Option) constructor with WithMessageProvider functional option
- MessageProvider interface for i18n; DefaultMessages (EN) and SpanishMessages (ES) built in
- ValidationErrors mapped to xerrors.ErrInvalidInput with field and tag context keys
- InvalidValidationError (non-struct input) mapped to xerrors.ErrInternal
- Full playground.ValidationErrors attached via WithError for callers needing all failures

Tested-via: todo-api POC integration
Reviewed-against: docs/adr/

go.mod

@@ -0,0 +1,18 @@
+module code.nochebuena.dev/go/valid
+
+go 1.25
+
+require (
+	code.nochebuena.dev/go/xerrors v0.9.0
+	github.com/go-playground/validator/v10 v10.30.1
+)
+
+require (
+	github.com/gabriel-vasile/mimetype v1.4.12 // indirect
+	github.com/go-playground/locales v0.14.1 // indirect
+	github.com/go-playground/universal-translator v0.18.1 // indirect
+	github.com/leodido/go-urn v1.4.0 // indirect
+	golang.org/x/crypto v0.46.0 // indirect
+	golang.org/x/sys v0.39.0 // indirect
+	golang.org/x/text v0.32.0 // indirect
+)