fix: 密码弹窗错误提示区域固定高度，避免显示/隐藏时窗口跳动

- SetPasswordModal: errorStyle 从 minHeight 改为固定 height，错误文本条件渲染改为占位渲染
- ResetPasswordModal: 同上

tauri-app/src/components/Modal/ResetPasswordModal.tsx

@@ -112,7 +112,9 @@ export default function ResetPasswordModal({ open, onClose }: ResetPasswordModal
     fontSize: '12px',
     color: '#e74c3c',
     marginTop: '4px',
-    minHeight: '18px',
+    height: '18px',
+    lineHeight: '18px',
+    overflow: 'hidden',
   };
 
   const pwdMismatch = confirmPassword.length > 0 && !pwdMatch;
@@ -243,7 +245,7 @@ export default function ResetPasswordModal({ open, onClose }: ResetPasswordModal
                 )}
               </button>
             </div>
-            {pwdTooShort && <div style={errorStyle}>密码至少需要6位</div>}
+            <div style={errorStyle}>{pwdTooShort ? '密码至少需要6位' : ''}</div>
           </div>
 
           {/* 确认密码 */}
@@ -286,7 +288,7 @@ export default function ResetPasswordModal({ open, onClose }: ResetPasswordModal
                 )}
               </button>
             </div>
-            {pwdMismatch && <div style={errorStyle}>两次输入的密码不一致</div>}
+            <div style={errorStyle}>{pwdMismatch ? '两次输入的密码不一致' : ''}</div>
           </div>
         </div>
 

tauri-app/src/components/Modal/SetPasswordModal.tsx

@@ -107,7 +107,9 @@ export default function SetPasswordModal({
     fontSize: '12px',
     color: '#e74c3c',
     marginTop: '4px',
-    minHeight: '18px',
+    height: '18px',
+    lineHeight: '18px',
+    overflow: 'hidden',
   };
 
   const pwdMismatch = confirmPassword.length > 0 && newPassword !== confirmPassword;
@@ -233,7 +235,7 @@ export default function SetPasswordModal({
                 )}
               </button>
             </div>
-            {pwdTooShort && <div style={errorStyle}>密码至少需要6位</div>}
+            <div style={errorStyle}>{pwdTooShort ? '密码至少需要6位' : ''}</div>
           </div>
 
           <div style={fieldStyle}>
@@ -276,7 +278,7 @@ export default function SetPasswordModal({
                 )}
               </button>
             </div>
-            {pwdMismatch && <div style={errorStyle}>两次输入的密码不一致</div>}
+            <div style={errorStyle}>{pwdMismatch ? '两次输入的密码不一致' : ''}</div>
           </div>
         </div>