✨ feat: implement input validation for API v2

- Added go-playground/validator dependency

- Created pkg/validation/ package with custom validator wrapper

- Implemented request validation for v2 greet endpoint

- Added structured validation error responses

- Extended BDD tests to cover validation scenarios

- Updated AGENTS.md with v2 API documentation

- Created ADR 0011-validation-library-selection.md

- Simplified server handler creation code

- Updated CHANGELOG with implementation details

go.mod

@@ -25,8 +25,12 @@ require (
 	github.com/cucumber/messages/go/v21 v21.0.1 // indirect
 	github.com/felixge/httpsnoop v1.0.4 // indirect
 	github.com/fsnotify/fsnotify v1.9.0 // indirect
+	github.com/gabriel-vasile/mimetype v1.4.13 // indirect
 	github.com/go-logr/logr v1.4.3 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
+	github.com/go-playground/locales v0.14.1 // indirect
+	github.com/go-playground/universal-translator v0.18.1 // indirect
+	github.com/go-playground/validator/v10 v10.30.2 // indirect
 	github.com/go-viper/mapstructure/v2 v2.4.0 // indirect
 	github.com/gofrs/uuid v4.4.0+incompatible // indirect
 	github.com/gogo/protobuf v1.3.1 // indirect
@@ -35,6 +39,7 @@ require (
 	github.com/hashicorp/go-immutable-radix v1.3.1 // indirect
 	github.com/hashicorp/go-memdb v1.3.5 // indirect
 	github.com/hashicorp/golang-lru v1.0.2 // indirect
+	github.com/leodido/go-urn v1.4.0 // indirect
 	github.com/mattn/go-colorable v0.1.14 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/pelletier/go-toml/v2 v2.2.4 // indirect
@@ -49,6 +54,7 @@ require (
 	go.opentelemetry.io/otel/metric v1.43.0 // indirect
 	go.opentelemetry.io/proto/otlp v1.10.0 // indirect
 	go.yaml.in/yaml/v3 v3.0.4 // indirect
+	golang.org/x/crypto v0.49.0 // indirect
 	golang.org/x/net v0.52.0 // indirect
 	golang.org/x/sys v0.42.0 // indirect
 	golang.org/x/text v0.35.0 // indirect