refactor: consolidate lang into constants, rename services to email

- Merge lang package into constants (add IsValidLang, ValidateLang, AllLangs)
- Rename internal/services to internal/email for consistency with pdf package
- Rename types to avoid redundancy: EmailService→Service, EmailConfig→Config
- Update all imports and references across codebase
- Delete internal/lang directory (functions moved to constants)

main.go

@@ -13,9 +13,10 @@ import (
 	"github.com/joho/godotenv"
 	"github.com/juanatsap/cv-site/internal/cache"
 	"github.com/juanatsap/cv-site/internal/config"
+	c "github.com/juanatsap/cv-site/internal/constants"
 	"github.com/juanatsap/cv-site/internal/handlers"
 	"github.com/juanatsap/cv-site/internal/routes"
-	"github.com/juanatsap/cv-site/internal/services"
+	"github.com/juanatsap/cv-site/internal/email"
 	"github.com/juanatsap/cv-site/internal/templates"
 )
 
@@ -51,7 +52,7 @@ func main() {
 	log.Println("📦 Data cache initialized (en, es)")
 
 	// Initialize email service
-	emailService := services.NewEmailService(&services.EmailConfig{
+	emailService := email.NewService(&email.Config{
 		SMTPHost:     cfg.Email.SMTPHost,
 		SMTPPort:     cfg.Email.SMTPPort,
 		SMTPUser:     cfg.Email.SMTPUser,
@@ -74,7 +75,7 @@ func main() {
 		Handler:      handler,
 		ReadTimeout:  time.Duration(cfg.Server.ReadTimeout) * time.Second,
 		WriteTimeout: time.Duration(cfg.Server.WriteTimeout) * time.Second,
-		IdleTimeout:  120 * time.Second,
+		IdleTimeout:  c.TimeoutIdleConnection,
 	}
 
 	// Start server in goroutine
@@ -104,7 +105,7 @@ func main() {
 		log.Printf("🛑 Shutdown signal received: %v", sig)
 
 		// Create shutdown context with timeout
-		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+		ctx, cancel := context.WithTimeout(context.Background(), c.TimeoutGracefulShutdown)
 		defer cancel()
 
 		// Attempt graceful shutdown of HTTP server