feat(auth): add change password API and frontend page

Backend:
- Add ChangePasswordReq DTO with validation (current + new password)
- Add AuthService::change_password() method with credential verification,
  password rehash, and token revocation
- Add POST /api/v1/auth/change-password endpoint with utoipa annotation

Frontend:
- Add changePassword() API function in auth.ts
- Add ChangePassword.tsx page with form validation and confirmation
- Add "修改密码" tab in Settings page

After password change, all refresh tokens are revoked and the user
is redirected to the login page.

apps/web/src/pages/Settings.tsx

@@ -7,6 +7,7 @@ import {
   SettingOutlined,
   BgColorsOutlined,
   AuditOutlined,
+  LockOutlined,
 } from '@ant-design/icons';
 import DictionaryManager from './settings/DictionaryManager';
 import LanguageManager from './settings/LanguageManager';
@@ -15,6 +16,7 @@ import NumberingRules from './settings/NumberingRules';
 import SystemSettings from './settings/SystemSettings';
 import ThemeSettings from './settings/ThemeSettings';
 import AuditLogViewer from './settings/AuditLogViewer';
+import ChangePassword from './settings/ChangePassword';
 
 const Settings: React.FC = () => {
   return (
@@ -100,6 +102,16 @@ const Settings: React.FC = () => {
             ),
             children: <AuditLogViewer />,
           },
+          {
+            key: 'change-password',
+            label: (
+              <span style={{ display: 'flex', alignItems: 'center', gap: 6 }}>
+                <LockOutlined style={{ fontSize: 14 }} />
+                修改密码
+              </span>
+            ),
+            children: <ChangePassword />,
+          },
         ]}
       />
     </div>