feat: add internal/auth package for credential-based login

internal/auth/prompt.go

@@ -0,0 +1,28 @@
+package auth
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+
+	"golang.org/x/term"
+)
+
+func PromptCredentials() (string, string, error) {
+	fmt.Print("Email: ")
+	line, err := bufio.NewReader(os.Stdin).ReadString('\n')
+	if err != nil {
+		return "", "", err
+	}
+	email := strings.TrimSpace(line)
+
+	fmt.Print("Password: ")
+	passwordBytes, err := term.ReadPassword(int(os.Stdin.Fd()))
+	fmt.Println()
+	if err != nil {
+		return "", "", err
+	}
+
+	return email, string(passwordBytes), nil
+}