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。

docs/README.md

@@ -29,6 +29,9 @@ GoodBuddy 文档按“文档类型 → 功能域”组织。新增文档应先
 ## 跨功能文档
 
 - [自动化平台架构](./architecture/automation-platform-architecture.md)
+- [平台功能页签与模型下载源设计](./architecture/model-download-source-design.md)
+- [本地文本向量模型与连接设计](./architecture/local-text-embedding-model-design.md)
+- [全双工实时语音交互设计](./architecture/full-duplex-voice-design.md)
 - [DeepSeek Harness Runtime 设计](./architecture/deepseek-harness-runtime-design.md)
 - [跨平台助手产品设计](./design/cross-platform-assistant-product-design.md)
 - [长期助手路线图](./roadmap/long-term-assistant-roadmap.md)