fix(module:steps): keep description below line when nzTitle is not set

components/steps/demo/description-only.md

@@ -0,0 +1,14 @@
+---
+order: 7
+title:
+  zh-CN: 仅描述
+  en-US: Description only
+---
+
+## zh-CN
+
+当不设置 `nzTitle` 时，仅展示描述。描述会固定显示在横线下方，不会与步骤条重叠。
+
+## en-US
+
+When `nzTitle` is not set, only the description is shown. The description always renders below the horizontal line and does not overlay the step bar.

components/steps/demo/description-only.ts

@@ -0,0 +1,18 @@
+import { Component } from '@angular/core';
+
+import { NzStepsModule } from 'ng-zorro-antd/steps';
+
+@Component({
+  selector: 'nz-demo-steps-description-only',
+  imports: [NzStepsModule],
+  template: `
+    <nz-steps [nzCurrent]="1">
+      <nz-step
+        nzDescription="This is a description only. The title row is reserved so the description stays below the horizontal line."
+      ></nz-step>
+      <nz-step nzTitle="In Progress" nzDescription="This step has both title and description."></nz-step>
+      <nz-step nzDescription="Another step with description only. No title provided."></nz-step>
+    </nz-steps>
+  `
+})
+export class NzDemoStepsDescriptionOnlyComponent {}

components/steps/doc/index.en-US.md

@@ -46,7 +46,7 @@ A single step in the step bar.
 | `[nzDescription]` | description of the step, optional property                                                                                                                 | `string \| TemplateRef<void>`                                                           | -        |
 | `[nzIcon]`        | icon of the step, optional property                                                                                                                        | `string \| string[] \| Set<string> \| { [klass: string]: any; }` \| `TemplateRef<void>` | -        |
 | `[nzStatus]`      | to specify the status. It will be automatically set by `nzCurrent` of `nz-steps` if not configured. Optional values are: `wait` `process` `finish` `error` | `'wait' \| 'process' \| 'finish' \| 'error'`                                            | `'wait'` |
-| `[nzTitle]`       | title of the step                                                                                                                                          | `string \| TemplateRef<void>`                                                           | -        |
+| `[nzTitle]`       | title of the step (optional). When omitted, only the description is shown and it renders below the horizontal line                                         | `string \| TemplateRef<void>`                                                           | -        |
 | `[nzSubtitle]`    | subTitle of the step                                                                                                                                       | `string \| TemplateRef<void>`                                                           | -        |
 | `[nzDisabled]`    | disable click                                                                                                                                              | `boolean`                                                                               | `false`  |
 | `[nzPercentage]`  | Progress percentage of the step in `process` status (only works on basic Steps)                                                                            | `number`                                                                                | -        |

components/steps/doc/index.zh-CN.md

@@ -47,7 +47,7 @@ description: 引导用户按照流程完成任务的导航条。
 | `[nzDescription]` | 步骤的详情描述，可选                                                                                                 | `string \| TemplateRef<void>`                                                           | -        |
 | `[nzIcon]`        | 步骤图标的类型，可选                                                                                                 | `string \| string[] \| Set<string> \| { [klass: string]: any; }` \| `TemplateRef<void>` | -        |
 | `[nzStatus]`      | 指定状态。当不配置该属性时，会使用 `nz-steps` 的 `nzCurrent` 来自动指定状态。可选：`wait` `process` `finish` `error` | `'wait' \| 'process' \| 'finish' \| 'error'`                                            | `'wait'` |
-| `[nzTitle]`       | 标题                                                                                                                 | `string \| TemplateRef<void>`                                                           | -        |
+| `[nzTitle]`       | 标题（可选）。不设置时仅展示描述，描述会显示在横线下方                                                               | `string \| TemplateRef<void>`                                                           | -        |
 | `[nzSubtitle]`    | 子标题                                                                                                               | `string \| TemplateRef<void>`                                                           | -        |
 | `[nzDisabled]`    | 禁用点击                                                                                                             | `boolean`                                                                               | `false`  |
 | `[nzPercentage]`  | 当前状态为 `process` 的步骤所显示的进度条进度（只对基本类型的 `nz-steps` 生效）                                      | `number`                                                                                | -        |

components/steps/step.component.ts

@@ -92,12 +92,17 @@ import { NzProgressFormatter, NzProgressModule } from 'ng-zorro-antd/progress';
         }
       </div>
       <div class="ant-steps-item-content">
-        <div class="ant-steps-item-title">
-          <ng-container *nzStringTemplateOutlet="nzTitle">{{ nzTitle }}</ng-container>
-          @if (nzSubtitle) {
-            <div class="ant-steps-item-subtitle">
-              <ng-container *nzStringTemplateOutlet="nzSubtitle">{{ nzSubtitle }}</ng-container>
-            </div>
+        <div
+          class="ant-steps-item-title"
+          [class.ant-steps-item-title-placeholder]="!nzTitle && !nzSubtitle && nzDescription"
+        >
+          @if (nzTitle !== null || nzSubtitle !== null) {
+            <ng-container *nzStringTemplateOutlet="nzTitle">{{ nzTitle }}</ng-container>
+            @if (nzSubtitle) {
+              <div class="ant-steps-item-subtitle">
+                <ng-container *nzStringTemplateOutlet="nzSubtitle">{{ nzSubtitle }}</ng-container>
+              </div>
+            }
           }
         </div>
         <div class="ant-steps-item-description">

components/steps/style/index.less

@@ -111,6 +111,11 @@
       background: @wait-tail-color;
       content: '';
     }
+
+    // When only description is provided, reserve title row so description stays below the line
+    &-placeholder {
+      min-height: @steps-title-line-height;
+    }
   }
 
   &-subtitle {