[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).

Look for the Local Inference UI component and the model loading logic. The feature involves adding a file chooser dialog and integrating local GGUF file loading into the existing model management flow. Check how models are currently downloaded and instantiated to understand the required changes.

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