flows status --cloud / flows logs: show running steps, add --watch and --follow

[khaliqgant]

Problem

flows status --cloud and flows logs are the user-facing way to inspect a hosted run, but they are built for finished runs.

• On a live run, status --cloud shows steps 0. That part depends on Cloud serving live step snapshots; see https://github.com/AgentWorkforce/cloud/issues/3921.
• flows logs <run> prints the runner output once and exits. There is no way to follow a run.

Proposal

1. flows status --cloud: render running, backoff, waiting and needs_human steps from Cloud's live snapshot, in the same grammar as the local flows status (↻ agent-5 (agent) running attempt 1/1 6m50s).
2. flows status --cloud --watch: redraw on an interval until the run is terminal, then print the final page once.
3. flows logs <run> --follow: poll and append new runner-output lines until the run is terminal. Since cloud#3918, runner output includes one line per step transition ([relayflow] ▶ agent-5 (agent) started, ✓ agent-1 … done in 5m16s · claude-opus-5 · 37 turns · $2.26 · wrote plan.md), so following it is useful even before live snapshots exist.

Acceptance

• --follow and --watch exit 0 when the run ends in success, and non-zero otherwise, using the same exit mapping as flows run.
• Both handle Ctrl-C cleanly and never print a partial frame.
• Tests use fake Cloud responses for a run that transitions running → completed.