feat: add explicit managed model download sources

Managed speech and OCR downloads previously used catalog-specific source URLs without a global selection. Platform Features now lets users choose ModelScope by default or Hugging Face, while Main validates and freezes that source for each download.

Verified coverage remains explicit: downloads never mix artifacts or silently switch sources, and installed models plus ZIP imports stay source-independent.

Release note: 可在“设置 → 平台功能 → 通用设置”中选择 ModelScope 或 Hugging Face 作为后续语音输入与 OCR 模型下载源；缺少完整已验证文件或下载失败时不会静默换源。

src/shared/contracts.ts

@@ -74,6 +74,7 @@ import type {
 import type {
   ApplicationSettings,
   ApplicationSettingsUpdate,
+  ModelDownloadSource,
   VersionCheckResult
 } from './application-settings-contracts'
 import type { ReleaseNotesSnapshot } from './release-notes-contracts'
@@ -1373,7 +1374,10 @@ export type DesktopApi = {
   }
   speechModels?: {
     getSnapshot: () => Promise<SpeechModelSnapshot>
-    install: (modelId: string) => Promise<SpeechModelSnapshot>
+    install: (
+      modelId: string,
+      expectedDownloadSource: ModelDownloadSource
+    ) => Promise<SpeechModelSnapshot>
     cancel: (modelId: string) => Promise<boolean>
     remove: (modelId: string) => Promise<SpeechModelSnapshot>
     select: (modelId: string | null) => Promise<SpeechModelSnapshot>
@@ -1405,7 +1409,8 @@ export type DesktopApi = {
       purpose: DocumentParsingTestPurpose
     ) => Promise<DocumentParsingDiagnostic | undefined>
     installOcrModel: (
-      modelId: string
+      modelId: string,
+      expectedDownloadSource: ModelDownloadSource
     ) => Promise<DocumentParsingSnapshot>
     cancelOcrModelOperation: (modelId: string) => Promise<boolean>
     removeOcrModel: (