[feat] Implement AssetService behind settings flag (#5404)

* [feat] add Comfy.Assets.UseAssetAPI to CORE_SETTINGS

* [feat] create AssetService

1. Add service for accessing new Asset API
2. Add fallback model paths logic so empty model directories appear for
   the user.
3. Copious tests for them all.

Co-Authored-By: Claude <noreply@anthropic.com>

* [feat] switch between assets and file paths for model data

* [feat] ignore assets with "missing" tag

* [fix] formatting and style

* [fix] call assets API with the correct filters

* [feat] elminate unused modelPath code

* [fix] remove stray comment

* [fix] model manager api was not parsed correctly

---------

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

tests-ui/tests/api.folderPaths.test.ts

@@ -0,0 +1,30 @@
+import axios from 'axios'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import { api } from '@/scripts/api'
+
+vi.mock('axios')
+
+describe('getFolderPaths', () => {
+  beforeEach(() => {
+    vi.resetAllMocks()
+  })
+
+  it('returns legacy API response when available', async () => {
+    const mockResponse = { checkpoints: ['/test/checkpoints'] }
+    vi.mocked(axios.get).mockResolvedValueOnce({ data: mockResponse })
+
+    const result = await api.getFolderPaths()
+
+    expect(result).toEqual(mockResponse)
+  })
+
+  it('returns empty object when legacy API unavailable (dynamic discovery)', async () => {
+    vi.mocked(axios.get).mockRejectedValueOnce(new Error())
+
+    const result = await api.getFolderPaths()
+
+    // With dynamic discovery, we don't pre-generate directories when API is unavailable
+    expect(result).toEqual({})
+  })
+})