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>

scripts/run.sh

@@ -24,7 +24,9 @@
 #   antigravity: `agy` on PATH with credentials already seeded (~/.gemini)
 #
 # Optional:
-#   MAX_DIFF_CHARS  diff truncation cap for the prompt (default 60000)
+#   MAX_DIFF_CHARS     diff truncation cap for the prompt (default 60000)
+#   GADFLY_STATUS_FILE per-model JSON path for the live status board (set by
+#                      entrypoint.sh; empty/unset disables status publishing)
 #
 # This script is advisory: it never fails the job for review content. It exits
 # non-zero only on a usage/configuration error.
@@ -161,6 +163,7 @@ case "$PROVIDER" in
           GADFLY_TITLE="$TITLE" \
           GADFLY_BODY="$BODY" \
           GADFLY_MAX_DIFF_CHARS="$MAX_DIFF_CHARS" \
+          GADFLY_STATUS_FILE="${GADFLY_STATUS_FILE:-}" \
           "$BIN" 2>"$ERR_FILE"
         )"
         rc=$?