dsh-quick-settings: Move settings entry from avatar menu to sidebar

`dsh-quick-settings` is a client-side plugin maintained by `logo20091001-ux`, version 0.1.4, licensed under the MIT license. It relocates the settings entry from the avatar menu to a persistent "⚙ Settings" row located above the account row in the sidebar footer. Clicking the button invokes the host's native `settings.open` command, mimicking the behavior of `Ctrl + ,` exactly; it involves no simulated clicks, DOM takeover, or kernel modification. Installation can be performed via the desktop "Settings → Plugins" menu by pasting `dsh-quick-settings`, or via the command line using `dsh plugin --profile web add dsh-quick-settings`. Note that the desktop Electron profile restricts management to the application level, so command-line installation will result in an error. The plugin relies on the `shortcuts` service and the `sidebar.footer.action` slot; if these dependencies are missing, the button will not render without affecting other interface elements. The author has confirmed successful operation on DSH 0.1.x Windows desktop.