feat(check): live progress TUI for multi check via PresenterActor (MULTI-1369)

[RobbieMcKinstry]

Surface what multi check is doing while it runs. A fourth, display-only
Kameo actor (PresenterActor) consumes a fire-and-forget UiEvent stream
emitted by the discovery/execution pipeline at each per-check milestone
(queued → started → retrying → settled) and renders progress through a
RenderBackend chosen at spawn from whether stdout is a TTY:

• InlineTuiBackend (TTY): a Ratatui inline viewport — a requirement→check
  tree + progress gauge with per-check spinners and climbing elapsed timers
  (the liveness signal). Completed requirements flush into permanent scrollback
  via insert_before as they finish, so the viewport only holds in-flight work
  and the full record persists by end-of-run with no separate reprint. Never
  uses the alternate screen.
• HeartbeatBackend (non-TTY): a slow-cadence one-line progress heartbeat on
  stderr so piped/CI runs show liveness. stdout is left untouched — the
  reporting actor's byte-for-byte report and 0/1 exit code are preserved exactly
  as MULTI-1368.
• NullBackend / RecordingBackend (tests): headless.

Events are a concrete enum (exhaustiveness, one Message impl, no per-message
boxing); polymorphism lives on the backend. A separate periodic Tick drives
redraws so animations keep moving between events. The presenter holds a single
PresenterState view-model with from-scratch tally scans (retry-safe), and the
flushed TTY record reuses the reporting actor's exact text + AND-aggregation, so
the TTY scrollback and non-TTY stdout differ only in inter-requirement order
(completion vs declaration), never per-requirement content.

Terminal restore is covered on all four paths: on_stop (normal/error), a panic
hook (panic), and an async-signal-safe SIGINT handler (Ctrl-C) that shows the
cursor and exits 130. The redraw ticker is owned by the actor and joined on stop.

Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com

[RobbieMcKinstry]

• feat(check): live progress TUI for multi check via PresenterActor (MULTI-1369) #146 👈 (View in Graphite)
• trunk

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