[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/components/UploadModelUrlInputCivitai.vue

@@ -0,0 +1,82 @@
+<template>
+  <div class="flex flex-col gap-6 text-sm text-muted-foreground">
+    <div class="flex flex-col gap-2">
+      <p class="m-0">
+        {{ $t('assetBrowser.uploadModelDescription1') }}
+      </p>
+      <ul class="list-disc space-y-1 pl-5 mt-0">
+        <li>
+          <i18n-t keypath="assetBrowser.uploadModelDescription2" tag="span">
+            <template #link>
+              <a
+                href="https://civitai.com/models"
+                target="_blank"
+                class="text-muted-foreground"
+              >
+                {{ $t('assetBrowser.uploadModelDescription2Link') }}
+              </a>
+            </template>
+          </i18n-t>
+        </li>
+        <li>
+          <i18n-t keypath="assetBrowser.uploadModelDescription3" tag="span">
+            <template #size>
+              <span class="font-bold italic">{{
+                $t('assetBrowser.maxFileSizeValue')
+              }}</span>
+            </template>
+          </i18n-t>
+        </li>
+      </ul>
+    </div>
+
+    <div class="flex flex-col gap-2">
+      <i18n-t keypath="assetBrowser.civitaiLinkLabel" tag="label" class="mb-0">
+        <template #download>
+          <span class="font-bold italic">{{
+            $t('assetBrowser.civitaiLinkLabelDownload')
+          }}</span>
+        </template>
+      </i18n-t>
+      <InputText
+        v-model="url"
+        autofocus
+        :placeholder="$t('assetBrowser.civitaiLinkPlaceholder')"
+        class="w-full bg-secondary-background border-0 p-4"
+        data-attr="upload-model-step1-url-input"
+      />
+      <p v-if="error" class="text-xs text-error">
+        {{ error }}
+      </p>
+      <i18n-t
+        v-else
+        keypath="assetBrowser.civitaiLinkExample"
+        tag="p"
+        class="text-xs"
+      >
+        <template #example>
+          <strong>{{ $t('assetBrowser.civitaiLinkExampleStrong') }}</strong>
+        </template>
+        <template #link>
+          <a
+            href="https://civitai.com/models/10706/luisap-z-image-and-qwen-pixel-art-refiner?modelVersionId=2225295"
+            target="_blank"
+            class="text-muted-foreground"
+          >
+            {{ $t('assetBrowser.civitaiLinkExampleUrl') }}
+          </a>
+        </template>
+      </i18n-t>
+    </div>
+  </div>
+</template>
+
+<script setup lang="ts">
+import InputText from 'primevue/inputtext'
+
+defineProps<{
+  error?: string
+}>()
+
+const url = defineModel<string>({ required: true })
+</script>