Improve email verification flow and error handling

- Send verification email before creating user to prevent orphaned accounts
- Detect SMTP authentication errors and fail fast without retries
- Add field-level validation errors for better frontend UX
- Configure docker-compose with explicit environment variables
- Document dollar sign escaping in .env.example (use $$)
- Implement welcome email on successful verification
- Clean up unnecessary comments

internal/application/commands/verify_email_handler.go

@@ -5,7 +5,9 @@ import (
 	"fmt"
 	"time"
 
+	"apocapoc-api/internal/domain/entities"
 	"apocapoc-api/internal/domain/repositories"
+	"apocapoc-api/internal/domain/services"
 	"apocapoc-api/internal/shared/errors"
 )
 
@@ -14,12 +16,20 @@ type VerifyEmailCommand struct {
 }
 
 type VerifyEmailHandler struct {
-	userRepo repositories.UserRepository
+	userRepo         repositories.UserRepository
+	emailService     services.EmailService
+	sendWelcomeEmail bool
 }
 
-func NewVerifyEmailHandler(userRepo repositories.UserRepository) *VerifyEmailHandler {
+func NewVerifyEmailHandler(
+	userRepo repositories.UserRepository,
+	emailService services.EmailService,
+	sendWelcomeEmail bool,
+) *VerifyEmailHandler {
 	return &VerifyEmailHandler{
-		userRepo: userRepo,
+		userRepo:         userRepo,
+		emailService:     emailService,
+		sendWelcomeEmail: sendWelcomeEmail,
 	}
 }
 
@@ -50,5 +60,27 @@ func (h *VerifyEmailHandler) Handle(ctx context.Context, cmd VerifyEmailCommand)
 		return fmt.Errorf("failed to verify email: %w", err)
 	}
 
+	if h.sendWelcomeEmail && h.emailService != nil {
+		h.sendWelcomeEmailToUser(user)
+	}
+
 	return nil
 }
+
+func (h *VerifyEmailHandler) sendWelcomeEmailToUser(user *entities.User) error {
+	emailBody := fmt.Sprintf(`
+		<h2>Welcome to Apocapoc!</h2>
+		<p>Your email has been successfully verified.</p>
+		<p>You can now start tracking your habits and building better routines.</p>
+		<p>If you have any questions or need help, please don't hesitate to contact us.</p>
+	`)
+
+	message := services.EmailMessage{
+		To:      user.Email,
+		Subject: "Welcome to Apocapoc!",
+		Body:    emailBody,
+		IsHTML:  true,
+	}
+
+	return h.emailService.Send(message)
+}