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/delete_user_handler.go

@@ -0,0 +1,39 @@
+package commands
+
+import (
+	"context"
+
+	"apocapoc-api/internal/domain/repositories"
+	"apocapoc-api/internal/shared/errors"
+)
+
+type DeleteUserCommand struct {
+	UserID string
+}
+
+type DeleteUserHandler struct {
+	userRepo repositories.UserRepository
+}
+
+func NewDeleteUserHandler(userRepo repositories.UserRepository) *DeleteUserHandler {
+	return &DeleteUserHandler{
+		userRepo: userRepo,
+	}
+}
+
+func (h *DeleteUserHandler) Handle(ctx context.Context, cmd DeleteUserCommand) error {
+	if cmd.UserID == "" {
+		return errors.ErrInvalidInput
+	}
+
+	user, err := h.userRepo.FindByID(ctx, cmd.UserID)
+	if err != nil {
+		return errors.ErrNotFound
+	}
+
+	if err := h.userRepo.Delete(ctx, user.ID); err != nil {
+		return err
+	}
+
+	return nil
+}