[Feature request]: Allow adding local GGUFs from disk

**What problem would this solve?**
It is incredibly wasteful to re-download gigabytes of data already present on the machine.
As well as it being near impossible on low-bandwidth networks.

**What would a good outcome look like?**
Being able to load GGUFs without having to _specifically_ download them through the app.

**Possible approaches**
Add a "Add local..." button to Local Inference to open a file chooser for GGUF.

**Additional context**
N/A

- [x] I have verified this does not duplicate an existing feature request

Do not begin implementation until the issue reaches **Ready** on the [Goose Issues board](https://github.com/orgs/aaif-goose/projects/1).

查找 Local Inference UI 组件和模型加载逻辑。该 feature 涉及添加 file chooser dialog，并将本地 GGUF 文件加载集成到现有的模型管理流程中。检查当前模型是如何下载和实例化的，以理解所需的更改。

由索引模型根据 Issue 内容生成。