[feat] Add HuggingFace model import support (#7540)

## Summary
Adds HuggingFace as a model import source alongside CivitAI, with
improved UX for model type selection and UTF-8 filename support.

## Changes
- **Import Sources**: Implemented extensible import source handler
pattern supporting both CivitAI and HuggingFace
- **UTF-8 Support**: Decode URL-encoded filenames to properly display
international characters (e.g., Chinese)
- **UX**: Sort model types alphabetically for easier selection
- **Feature Flag**: Added `huggingfaceModelImportEnabled` flag for
gradual rollout
- **i18n**: Use proper template parameters for localized error messages

## Technical Details
- Created `ImportSourceHandler` interface for extensibility
- Refactored existing CivitAI logic into handler pattern
- Added URL validation per source
- Filename decoding handles malformed URLs gracefully

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7540-feat-Add-HuggingFace-model-import-support-2cb6d73d3650818f966cca89244e8c36)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: GitHub Action <action@github.com>

src/platform/assets/utils/importSourceUtil.ts

@@ -0,0 +1,15 @@
+import type { ImportSource } from '@/platform/assets/types/importSource'
+
+/**
+ * Check if a URL belongs to a specific import source
+ */
+export function validateSourceUrl(url: string, source: ImportSource): boolean {
+  try {
+    const hostname = new URL(url).hostname.toLowerCase()
+    return source.hostnames.some(
+      (h) => hostname === h || hostname.endsWith(`.${h}`)
+    )
+  } catch {
+    return false
+  }
+}