Support multiple saved servers in the desktop menu

[SawyerHood]

Human comments

What was wrong

The desktop Window → Server menu stored only one custom server URL, so connecting to another machine replaced the previously saved address.

What changed

Added an Add Server… action and a persisted list of custom server URLs. Each saved machine can be selected independently, duplicate URLs select the existing entry, and Set Server URL… edits or removes the last selected custom entry without losing the others. Existing single-server preferences migrate automatically. Updated desktop documentation and regression tests. No server/daemon wire changes.

How you verified

• Turbo desktop build and typecheck passed; focused server-target, server-moved, and menu suites passed all 71 tests. Formatting and diff checks passed.
• Ran an isolated real Electron instance against local fixture servers using native menu callbacks and keyboard input through the actual URL dialog/preload. Verified adding, switching, invalid URLs, cancellation, normalization/deduplication, editing, removal, and saved selection/list persistence across a full Electron restart. Inspected dialog screenshots and cleaned up the fixture processes/profile.
• Physical macOS menu clicking was not exercised because this host lacks Accessibility permission. The initial broad Electron smoke run hit local binary extraction and Keychain startup issues; the dedicated flow above passed with Electron's mock-keychain flag.

AGENT GENERATED