feat: add downloadable release management for desktop client

- Extend DesktopClientReleaseCheckResponse with platform, arch, and channel fields.
- Introduce DesktopClientDownloadableRelease and DesktopClientDownloadableReleaseListResponse interfaces for managing downloadable releases.
- Implement ListDownloadable method in DesktopClientReleaseService to retrieve downloadable releases based on the specified channel.
- Update DesktopClientReleaseCheckResult to include platform, arch, and channel information.
- Add resolveInstallerDownloadURL method to handle download URL resolution for releases.
- Create new endpoint in DesktopReleaseHandler for listing downloadable releases.
- Update router to include the new downloadable releases route.
- Enhance tests to cover the new functionality for resolving download URLs and listing downloadable releases.

apps/admin-web/src/components/kol/KolVariableConfig.vue

@@ -254,13 +254,11 @@ defineExpose({
 
         <div v-if="variable.type !== 'checkbox' && variable.type !== 'select'" class="form-item">
           <label>{{ t('kol.manage.variable.placeholder') }}</label>
-          <a-input
+          <a-textarea
             :value="variable.placeholder"
             size="small"
-            @input="
-              (e: Event) =>
-                updateVariable(index, { placeholder: (e.target as HTMLInputElement).value })
-            "
+            :rows="3"
+            @update:value="(val: string) => updateVariable(index, { placeholder: val })"
           />
         </div>