dsh-model-source-picker: A two-level selector for first selecting the model source and then selecting the model

Introducing the DSH plugin dsh-model-source-picker maintained by BEAVER-awa. It modifies the model selection in the input box to a Provider-first two-level structure, shares modelDirectories with /model, and requires only client-side UI. It includes official installation commands, interaction instructions, diagnostic and uninstallation methods. It requires DSH ≥ 0.2.1 and Node ≥ 22 and is licensed under the MIT License.