lzlrt/dsha-desktop-link

Adds one button to the sidebar foot that opens the desktop DSH Web GUI — in the system browser on a phone, in a new tab on a desktop. The target address is read from plugin config, DSH_DESKTOP_URL, or ~/.dsh/desktop-url.txt, and falls back to the relay origin published by dsh-remote-web-ui; the button renders inert with a hint when nothing is configured. It also adds a small gear button that saves the address into ~/.dsh/desktop-url.txt; on a phone with no separate launch address set, a click asks the local pairing service (/api/pair/issue) for a one-time pairing link and opens it; its HTTP routes (/api/desktop-link/…) have no DSH access check.