The footer pill fired OpenWorkerConnectionHelpCommand unconditionally, so
clicking it on a connected worker showed the "WORKER NOT REACHABLE" dialog.
Gate the command on !IsConnected (not IsOffline — the retry loop stays in
"connecting" forever while the worker is down, which is exactly when the
dialog's "Start Worker" is needed) and re-evaluate CanExecute on connection
state changes.
Adds ShowWorkerConnectionModal hook, DecideShowConnectionPrompt one-shot gate, OpenWorkerConnectionHelp relay command, and a 12 s _connectTimer to IslandsShellViewModel; covered by two new unit tests.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>