✨ 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

pkg/server/server.go

@@ -10,6 +10,7 @@ import (
 
 	"DanceLessonsCoach/pkg/config"
 	"DanceLessonsCoach/pkg/greet"
+	"DanceLessonsCoach/pkg/validation"
 	"DanceLessonsCoach/pkg/telemetry"
 	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
 	sdktrace "go.opentelemetry.io/otel/sdk/trace"
@@ -20,19 +21,29 @@ import (
 )
 
 type Server struct {
-	router      *chi.Mux
-	readyCtx    context.Context
-	withOTEL    bool
-	config      *config.Config
+	router         *chi.Mux
+	readyCtx       context.Context
+	withOTEL       bool
+	config         *config.Config
 	tracerProvider *sdktrace.TracerProvider
+	validator      *validation.Validator
 }
 
 func NewServer(cfg *config.Config, readyCtx context.Context) *Server {
+	// Create validator instance
+	validator, err := validation.GetValidatorFromConfig(cfg)
+	if err != nil {
+		log.Error().Err(err).Msg("Failed to create validator, continuing without validation")
+	} else {
+		log.Trace().Msg("Validator created successfully")
+	}
+
 	s := &Server{
-		router:   chi.NewRouter(),
-		readyCtx: readyCtx,
-		withOTEL: cfg.GetTelemetryEnabled(),
-		config:   cfg,
+		router:    chi.NewRouter(),
+		readyCtx:  readyCtx,
+		withOTEL:  cfg.GetTelemetryEnabled(),
+		config:    cfg,
+		validator: validator,
 	}
 	s.setupRoutes()
 	return s
@@ -76,7 +87,7 @@ func (s *Server) registerApiV1Routes(r chi.Router) {
 
 func (s *Server) registerApiV2Routes(r chi.Router) {
 	greetServiceV2 := greet.NewServiceV2()
-	greetHandlerV2 := greet.NewApiV2GreetHandler(greetServiceV2)
+	greetHandlerV2 := greet.NewApiV2GreetHandler(greetServiceV2, s.validator)
 	r.Route("/greet", func(r chi.Router) {
 		greetHandlerV2.RegisterRoutes(r)
 	})