feat(user): argon2id password hashing helpers

internal/user/auth_test.go

@@ -0,0 +1,26 @@
+package user
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestHashAndVerifyPassword(t *testing.T) {
+	hash, err := HashPassword("hello-world-12345")
+	require.NoError(t, err)
+	require.NotEmpty(t, hash)
+
+	ok, err := VerifyPassword("hello-world-12345", hash)
+	require.NoError(t, err)
+	require.True(t, ok)
+
+	bad, err := VerifyPassword("wrong", hash)
+	require.NoError(t, err)
+	require.False(t, bad)
+}
+
+func TestHashPassword_RejectsTooShort(t *testing.T) {
+	_, err := HashPassword("short")
+	require.Error(t, err)
+}