feat: add user password management

chfs-ng/internal/auth/users.go

@@ -109,6 +109,19 @@ func (u *UserStore) Add(m *Manager, username, password, home string) (*Account,
 	return a, u.Save(m)
 }
 
+func (u *UserStore) UpdatePassword(m *Manager, username, password string) error {
+	if strings.TrimSpace(password) == "" {
+		return fmt.Errorf("password required")
+	}
+	a, ok := m.Accounts[username]
+	if !ok || a.PasswordHash == "" {
+		return fmt.Errorf("managed user not found")
+	}
+	a.PasswordHash = PasswordHash(password)
+	a.Password = ""
+	return u.Save(m)
+}
+
 func (u *UserStore) Delete(m *Manager, username string) error {
 	a, ok := m.Accounts[username]
 	if !ok || a.Admin || a.PasswordHash == "" {