cmux: restored SSH (cmux-tui) tabs stuck on "Mac disconnected" with a no-op Retry

In cmux (manaflow-ai/cmux), a cmux-tui SSH workspace restores every terminal snapshot that has no saved surfaceProjections record as a process-free device display pane (Workspace.createPanel, added in 5f0d222). Nothing ever reattaches such a pane, because CmuxTuiSurfaceProvider.reprojectRestoredPanes only walks catalog projections. Its Retry guards on SurfaceCatalog.projection(forPanel:) and returns silently. These panes usually come from Cmd+T while a file preview is the selected tab: cloudTerminalSourcePlacement returns nil there, so cmux opens a local shell. To diagnose, check the session JSON: such panels have a local ttyName and no surfaceProjections entry. Workaround: close them and make new tabs with Cmd+T from a live remote tab. Upstream PR #14238, which restored them as local shells, was closed by design (an SSH workspace never starts a local shell).