fix: dashboard add minimum height to panel container for better layout (#8773)

### **PR Type**
Bug fix


___

### **Description**
- Add min-height to panel container

- Prevent collapsed layout on small content

- Improve dashboard panel visual consistency


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### Diagram Walkthrough


```mermaid
flowchart LR
  AddPanel["AddPanel.vue container"] -- "add tw-min-h-[140px]" --> StableLayout["Consistent panel height"]
```



<details> <summary><h3> File Walkthrough</h3></summary>

<table><thead><tr><th></th><th align="left">Relevant
files</th></tr></thead><tbody><tr><td><strong>Bug
fix</strong></td><td><table>
<tr>
  <td>
    <details>
<summary><strong>AddPanel.vue</strong><dd><code>Add minimum height to
panel container</code>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
&nbsp; &nbsp; &nbsp; </dd></summary>
<hr>

web/src/views/Dashboards/addPanel/AddPanel.vue

<ul><li>Add Tailwind class <code>tw-min-h-[140px]</code> to
container<br> <li> Keep existing dynamic height
<code>tw-h-[calc(100vh-500px)]</code><br> <li> Improve layout stability
for panel renderer area</ul>


</details>


  </td>
<td><a
href="https://github.com/openobserve/openobserve/pull/8773/files#diff-c9632db1ad95af95aba10161bcbc7c5608318919f228637bdafae3f3a31267e8">+1/-1</a>&nbsp;
&nbsp; &nbsp; </td>

</tr>
</table></td></tr></tr></tbody></table>

</details>

___

web/src/views/Dashboards/addPanel/AddPanel.vue

@@ -239,7 +239,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
                       />
                     </span>
                   </div>
-                  <div class="tw-h-[calc(100vh-500px)]">
+                  <div class="tw-h-[calc(100vh-500px)] tw-min-h-[140px]">
                     <PanelSchemaRenderer
                       v-if="chartData"
                       @metadata-update="metaDataValue"