Add an interactive TUI for parallel task runs

[mbullington]

Problem

Parallel runs are hard to follow in streaming output. Status lines and child-process logs interleave, and it takes work to answer basic questions such as which tasks are running, which tasks were cached, and which task failed.

Remy's deploy:all:dev has a useful dashboard, but its full-screen repaint and status-grouped layout cause visible jitter. Turborepo's terminal UI provides another useful reference, especially its per-task output view.

Proposal

Add an optional interactive TUI to scripts run.

The scheduler should emit task lifecycle and output events to a reporter. Keep the current line-oriented reporter for non-interactive use, and add a TUI reporter for terminals.

Suggested behavior:

• Keep tasks in a stable order while their status changes in place.
• Show pending, running, cached, succeeded, failed, and skipped states.
• Show elapsed time for running and completed tasks.
• Capture output per task and provide a selectable log pane or tabbed pager.
• Render on lifecycle events, with a low-frequency timer only for elapsed time.
• Use terminal cell diffing instead of clearing and repainting the full screen.
• Restore terminal state after success, failure, panic, or interruption.
• Print a durable plain-text summary after leaving the alternate screen.
• Preserve line-oriented output for CI, redirected output, and unsupported terminals.

A CLI such as --ui=auto|tui|stream would keep behavior explicit. auto could select the TUI only when the relevant streams are terminals.

Acceptance criteria

• Parallel tasks have a stable, non-jittering task list.
• A user can inspect output from each task while the run is active.
• Cached tasks are distinguishable from tasks executed during the run.
• --ui=stream retains composable, line-oriented output.
• Non-TTY environments never emit cursor-control sequences.
• Ctrl-C and failures leave the terminal usable and preserve useful diagnostics.