[feat] Add Civitai model upload wizard (#6694)

## Summary
Adds a complete model upload workflow that allows users to import models
from Civitai URLs directly into their library.

## Changes
- **Multi-step wizard**: URL input → metadata confirmation → upload
progress
- **Components**: UploadModelDialog, UploadModelUrlInput,
UploadModelConfirmation, UploadModelProgress, UploadModelDialogHeader
- **API integration**: New assetService methods for metadata retrieval
and URL-based uploads
- **Model type management**: useModelTypes composable for fetching and
formatting available model types
- **UX improvements**: Optional validation bypass for UrlInput component
- **Localization**: 26 new i18n strings for the upload workflow

## Review Focus
- Error handling for failed uploads and metadata retrieval
- Model type detection and selection logic
- Dialog state management across multi-step workflow

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6694-feat-Add-Civitai-model-upload-wizard-2ab6d73d36508193b3b1dd67c7cc5a09)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Claude <noreply@anthropic.com>

src/platform/assets/components/UploadModelDialogHeader.vue

@@ -0,0 +1,12 @@
+<template>
+  <div class="flex items-center gap-3 px-4 py-2 font-bold">
+    <span>{{ $t('assetBrowser.uploadModelFromCivitai') }}</span>
+    <span
+      class="rounded-full bg-white px-1.5 py-0 text-xxs font-medium uppercase text-black"
+    >
+      {{ $t('g.beta') }}
+    </span>
+  </div>
+</template>
+
+<script setup lang="ts"></script>