feat: live status-board comment — per-model/per-lens review progress

Phase 3 of the gadfly-games build. With several models × several lenses
reviewing a PR, all you'd see mid-run is a row of "⏳ Reviewing…"
placeholders. Add ONE consolidated, live-updating status-board comment
that aggregates every model's per-lens progress (queued → running →
finished + verdict), so progress is visible at a glance and a watcher
can tell when the whole swarm is done.

- cmd/gadfly: opt-in statusWriter (GADFLY_STATUS_FILE) publishes this
  model's lenses to a JSON file, written atomically (temp+rename) as
  runSpecialists transitions each lens. Inert when unset — plain runs
  and tests are unaffected.
- scripts/status-board.sh: background renderer that polls the status
  dir and upserts one marker comment every GADFLY_STATUS_POLL_SECS
  (default 12s), caching the comment id to PATCH in place. Advisory and
  best-effort; the per-model findings comments are untouched.
- entrypoint.sh: pre-seeds every model as queued, launches the board,
  waits only on the review lanes, then signals .done for a final render.
  Default on; disable with GADFLY_STATUS_BOARD=0.
- Docs: README config table + "Live status board" section, example
  stub note, CLAUDE.md architecture map.

gofmt clean, go vet quiet, go build + go test -race green.

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

CLAUDE.md

@@ -39,6 +39,7 @@ cmd/gadfly/            the reviewer binary — pure producer of review markdown
   recheck.go           second-pass verification prompt + verdict recompute
   *_test.go            sandbox, recheck, wrap-up, spec/endpoint-parse, specialist-resolution tests
 scripts/run.sh         fetch PR diff+meta, run the binary, upsert ONE labeled PR comment
+scripts/status-board.sh    render+upsert ONE live status-board comment (per-model/per-lens progress)
 scripts/system-prompt.txt   the reviewer persona + verification discipline (generic, not repo-specific)
 entrypoint.sh          container brains: trigger gating, PR clone, model loop (the logic that
                        used to live in workflow YAML)