feat: remove obsolete model asset feature flags (#8566)

## Summary
Remove feature flags that are now enabled for all users and clean up
dead code paths.

## Changes

**Removed feature flags:**
- `huggingfaceModelImportEnabled` - always show generic URL input with
both Civitai/HuggingFace support
- `assetDeletionEnabled` - delete button always shown for mutable assets
- `asyncModelUploadEnabled` - always use async upload path (removed sync
upload and file size warnings)

**Kept feature flags:**
- `modelUploadButtonEnabled` - controls upload button visibility (local
vs cloud)
- `privateModelsEnabled` - controls upgrade modal vs upload dialog

**Deleted unused component:**
- `UploadModelUrlInputCivitai.vue` (replaced by generic input)

## Testing
- `pnpm typecheck` passes
- `pnpm lint` passes

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8566-feat-remove-obsolete-model-asset-feature-flags-2fc6d73d365081149ec6e78d995c8a44)
by [Unito](https://www.unito.io)


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

## Release Notes

* **Improvements**
  * Asset deletion option is now always available
  * Model upload experience simplified with unified import flow
  * Model uploads now consistently use asynchronous processing
  * HuggingFace model imports are now always supported

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Co-authored-by: Amp <amp@ampcode.com>

src/composables/useFeatureFlags.ts

@@ -15,13 +15,10 @@ export enum ServerFeatureFlag {
   MAX_UPLOAD_SIZE = 'max_upload_size',
   MANAGER_SUPPORTS_V4 = 'extension.manager.supports_v4',
   MODEL_UPLOAD_BUTTON_ENABLED = 'model_upload_button_enabled',
-  ASSET_DELETION_ENABLED = 'asset_deletion_enabled',
   ASSET_RENAME_ENABLED = 'asset_rename_enabled',
   PRIVATE_MODELS_ENABLED = 'private_models_enabled',
   ONBOARDING_SURVEY_ENABLED = 'onboarding_survey_enabled',
-  HUGGINGFACE_MODEL_IMPORT_ENABLED = 'huggingface_model_import_enabled',
   LINEAR_TOGGLE_ENABLED = 'linear_toggle_enabled',
-  ASYNC_MODEL_UPLOAD_ENABLED = 'async_model_upload_enabled',
   TEAM_WORKSPACES_ENABLED = 'team_workspaces_enabled',
   USER_SECRETS_ENABLED = 'user_secrets_enabled'
 }
@@ -41,7 +38,6 @@ export function useFeatureFlags() {
       return api.getServerFeature(ServerFeatureFlag.MANAGER_SUPPORTS_V4)
     },
     get modelUploadButtonEnabled() {
-      // Check remote config first (from /api/features), fall back to websocket feature flags
       return (
         remoteConfig.value.model_upload_button_enabled ??
         api.getServerFeature(
@@ -50,12 +46,6 @@ export function useFeatureFlags() {
         )
       )
     },
-    get assetDeletionEnabled() {
-      return (
-        remoteConfig.value.asset_deletion_enabled ??
-        api.getServerFeature(ServerFeatureFlag.ASSET_DELETION_ENABLED, false)
-      )
-    },
     get assetRenameEnabled() {
       return (
         remoteConfig.value.asset_rename_enabled ??
@@ -63,7 +53,6 @@ export function useFeatureFlags() {
       )
     },
     get privateModelsEnabled() {
-      // Check remote config first (from /api/features), fall back to websocket feature flags
       return (
         remoteConfig.value.private_models_enabled ??
         api.getServerFeature(ServerFeatureFlag.PRIVATE_MODELS_ENABLED, false)
@@ -75,30 +64,12 @@ export function useFeatureFlags() {
         api.getServerFeature(ServerFeatureFlag.ONBOARDING_SURVEY_ENABLED, true)
       )
     },
-    get huggingfaceModelImportEnabled() {
-      return (
-        remoteConfig.value.huggingface_model_import_enabled ??
-        api.getServerFeature(
-          ServerFeatureFlag.HUGGINGFACE_MODEL_IMPORT_ENABLED,
-          false
-        )
-      )
-    },
     get linearToggleEnabled() {
       return (
         remoteConfig.value.linear_toggle_enabled ??
         api.getServerFeature(ServerFeatureFlag.LINEAR_TOGGLE_ENABLED, false)
       )
     },
-    get asyncModelUploadEnabled() {
-      return (
-        remoteConfig.value.async_model_upload_enabled ??
-        api.getServerFeature(
-          ServerFeatureFlag.ASYNC_MODEL_UPLOAD_ENABLED,
-          false
-        )
-      )
-    },
     /**
      * Whether team workspaces feature is enabled.
      * IMPORTANT: Returns false until authenticated remote config is loaded.