PR 3930 release candidate (c3d0b79)

Release candidate of PR 3930 (Lemonade Nexus) from branch commit c3d0b79, built by CI run 42736721962, with the Nexus SDK at lemonade-nexus aebe65e.

This is a pre-release for testing the PR. It is not a Lemonade release.

New in this build:

• A browser can enable Mesh on a device whose account still holds a passkey registered earlier through the desktop app. Enable Mesh moves the device to its device key once that key has authenticated, and lemond retires the passkey. The earlier build stopped at "Open the Lemonade desktop app on this computer to verify your passkey" whether lemond ran as root, as a user or as a service.

From the previous builds: browser Enable Mesh on packaged Linux servers with the system device key, greyed-out mesh hosts without a connection, relay failures with their reason, Genesis key discovery that names each server's answer, LAN addresses fastest link first, the host-grouped chat model picker, "Chat runs on" in the account menu, the server info dialog, the mesh port keeping its certificate across restarts, and Ubuntu 26.04 packages.