dsh-api-key-switch: Save multiple API keys in the settings panel and one-click switch.

Maintenance update my-0228 for the DSH Web plugin adds a new "API Key Switching" page to the settings panel. It stores multiple API keys in the local credential database; clicking "Use" in the list switches the active key, taking effect on the next model request without requiring a DSH restart. Keys are displayed masked, and switching writes to the default DEEPSEEK_API_KEY credential reference, which is written atomically by the DSH credential service. The article verifies the installation commands, the ref configuration for the Cordis patch, the fix script for .credentials.yaml record shapes and illegal record keys, as well as validation rules and known edge cases. It also notes that the plugin runs with the current DSH process permissions and advises checking the source code and MIT license before installation.