dsh-arrowkey-nav: Arrow Key Navigation for DSH Web GUI

The DSH Web GUI plugin `dsh-arrowkey-nav` allows users to quickly navigate between sessions and workspaces using keyboard arrow keys instead of clicking or pasting commands. Core features include switching sessions up and down, switching workspaces left and right, automatic scrolling, focus retention, and edge looping. Installation requires running a specific command and supports DSH versions 0.1.0 through 0.2.0. The plugin works by reading the sidebar order via the client controller and is not limited by DOM IDs. Collapsed views, IME capture, and editor draft states are known to restrict some functionality.