fix(upload-model): UI/UX improvements for Upload Model Dialog (#7969)

## Summary

Addresses UI/UX feedback on the Upload Model Dialog (BYOM feature).

## Changes

1. **Standardize link styling** - Use consistent `text-muted-foreground
underline` for all links in both URL input variants
2. **Increase warning/example text font size** - Changed from 12px
(`text-xs`) to 14px (`text-sm`) for better readability
3. **Fix padding inconsistency** - Aligned padding between model name
box and SingleSelect dropdown; moved "Not sure?" help text inline with
the label
4. **Add "Upload Another" button** - Allows users to upload multiple
models without closing and reopening the dialog

## Testing

- Verified link styling consistency across both Civitai and generic URL
input components
- Confirmed padding alignment in confirmation step
- Tested Upload Another button resets wizard to step 1

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7969-fix-upload-model-UI-UX-improvements-for-Upload-Model-Dialog-2e66d73d3650815c8184cedb3d02672d)
by [Unito](https://www.unito.io)

src/platform/assets/components/UploadModelDialog.vue

@@ -48,6 +48,7 @@
       @fetch-metadata="handleFetchMetadata"
       @upload="handleUploadModel"
       @close="handleClose"
+      @import-another="resetWizard"
     />
   </div>
 </template>
@@ -85,7 +86,8 @@ const {
   canUploadModel,
   fetchMetadata,
   uploadModel,
-  goToPreviousStep
+  goToPreviousStep,
+  resetWizard
 } = useUploadModelWizard(modelTypes)
 
 async function handleFetchMetadata() {