[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/UploadModelUrlInput.vue

@@ -1,28 +1,74 @@
 <template>
-  <div class="flex flex-col gap-6 text-sm text-muted-foreground">
-    <div class="flex flex-col gap-2">
-      <p class="m-0">
-        {{ $t('assetBrowser.uploadModelDescription1') }}
-      </p>
-      <ul class="list-disc space-y-1 pl-5 mt-0">
-        <li v-html="$t('assetBrowser.uploadModelDescription2')" />
-        <li v-html="$t('assetBrowser.uploadModelDescription3')" />
-      </ul>
+  <div class="flex flex-col justify-between h-full gap-6 text-sm">
+    <div class="flex flex-col gap-6">
+      <div class="flex flex-col gap-2">
+        <p class="m-0 text-foreground">
+          {{ $t('assetBrowser.uploadModelDescription1Generic') }}
+        </p>
+        <div class="m-0">
+          <p class="m-0 text-muted-foreground">
+            {{ $t('assetBrowser.uploadModelDescription2Generic') }}
+          </p>
+          <span class="inline-flex items-center gap-1 flex-wrap mt-2">
+            <span class="inline-flex items-center gap-1">
+              <img
+                :src="civitaiIcon"
+                :alt="$t('assetBrowser.providerCivitai')"
+                class="w-4 h-4"
+              />
+              <a
+                :href="civitaiUrl"
+                target="_blank"
+                rel="noopener noreferrer"
+                class="text-muted underline"
+              >
+                {{ $t('assetBrowser.providerCivitai') }}</a
+              ><span>,</span>
+            </span>
+            <span class="inline-flex items-center gap-1">
+              <img
+                :src="huggingFaceIcon"
+                :alt="$t('assetBrowser.providerHuggingFace')"
+                class="w-4 h-4"
+              />
+              <a
+                :href="huggingFaceUrl"
+                target="_blank"
+                rel="noopener noreferrer"
+                class="text-muted underline"
+              >
+                {{ $t('assetBrowser.providerHuggingFace') }}
+              </a>
+            </span>
+          </span>
+        </div>
+      </div>
+
+      <div class="flex flex-col gap-2">
+        <InputText
+          v-model="url"
+          autofocus
+          :placeholder="$t('assetBrowser.genericLinkPlaceholder')"
+          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>
+        <p v-else class="text-foreground">
+          <i18n-t keypath="assetBrowser.maxFileSize" tag="span">
+            <template #size>
+              <span class="font-bold italic">{{
+                $t('assetBrowser.maxFileSizeValue')
+              }}</span>
+            </template>
+          </i18n-t>
+        </p>
+      </div>
     </div>
 
-    <div class="flex flex-col gap-2">
-      <label class="mb-0" v-html="$t('assetBrowser.civitaiLinkLabel')"> </label>
-      <InputText
-        v-model="url"
-        autofocus
-        :placeholder="$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>
-      <p v-else v-html="$t('assetBrowser.civitaiLinkExample')"></p>
+    <div class="text-sm text-muted">
+      {{ $t('assetBrowser.uploadModelHelpFooterText') }}
     </div>
   </div>
 </template>
@@ -44,4 +90,9 @@ const url = computed({
   get: () => props.modelValue,
   set: (value: string) => emit('update:modelValue', value)
 })
+
+const civitaiIcon = '/assets/images/civitai.svg'
+const civitaiUrl = 'https://civitai.com/models'
+const huggingFaceIcon = '/assets/images/hf-logo.svg'
+const huggingFaceUrl = 'https://huggingface.co'
 </script>